Cake and Icing:
Well, you've got to have these two things to be able to decorate a cake! If you're unfamiliar with my cakes, I just have to mention that I try to make things as easy as possible. I like made-from-scratch cakes as much as the next person, but I spend a lot of time on decorating the cakes. I am like many people who have a hard enough time trying to carve out a chunk of time to be with their families, so when it comes to a cake project, I embrace shortcuts and simply use boxed cake mix and canned icing - something anyone can just pick up at the store. You could certainly make your cake and icing from scratch and go from there but the results you see in the pictures, unless otherwise noted, are from boxed cake mix and canned icing.
If I plan to do a lot of carving to the cake, I add some all-purpose flour to the batch to firm it up - sometimes a couple of Tablespoons and sometimes (since I've moved to a high altitude) I add as much as 1/4 cup.
For icing, I usually stick with Pillsbury icing, but I've found that it really doesn't matter. If I need a white cake, I definitely choose the Pillsbury Classic White over the Vanilla (which has a slightly off-white color). If I need black icing, I start with Milk Chocolate, Chocolate Fudge or any chocolate variation of icing so I can use less black coloring.
Regular store bought canned icing is not nearly as thick as buttercream icing so you won't be able to create icing designs that "stand up" like fancy flowers. With canned icing, those flowers would look wilted. You can certainly add some powered sugar to it and mix it in, but you would also need to add some flavoring because your icing would wind up just tasting like sugar. If you have to do all that, you might as well make buttercream icing!
Cake Pans:
I have a variety of cake pans that I use for my various projects. Sometimes I think I have too many, but I know a professional cake decorator that has over 300 different cake pans in her collection. Many of her cake pans are character pans, but there are the tiered sizes in several shapes as well.
If the only pan you have for baking cakes is a 13x9 inch pan, you'll be just fine. There are plenty of cakes to make using this size pan.
Featured cakes that use a 13x9 inch pan are: Electric Guitar Cake, Unicorn Cake, Movie Script Cake, "Fade In" Movie Script Cake, Lego Mini-figure Cake, Bowling Themed Cake, Tiki Man Cake, X-Box Controller Cake, Conan's Atlantean Sword, Pikmin Cake, Kingdom Hearts 2 Keyblade Cake

These are getting harder to find. If you must have one, you may have to search on eBay. Otherwise, try baking your cake in an oven-safe bowl. If you have one of these and have lost the instruction book, there is one available for printing and download at Bakenfill.com.
Featured cakes using the Betty Crocker Bake 'N Fill Cake Pan are: Cinderella Carriage Cake, Super Mario Mushroom Cake, Princess Cake, Basketball Cake, Baby Dragon Cake, Sombrero Cake

My Bundt Pan is a Nordicware Bundt Pan. It is heavy and durable and has a non-stick coating in it (but please don't skip the grease and flour stage of baking).
Featured cakes that use a Bundt Pan pan are: Pumpkin Cake

Featured cakes that use a Round cake pan are: Ladybug Cake, Butterfly Cake, Ferret Cake, Bumblebee Cake, Grill Cake, Dragon Cake, Bowling Cake

I happened to acquire 2 mini-muffin pans when I found myself making over 100 mini cupcakes for a friend's bridal shower. You really don't need two of them - unless you find yourself in the same predicament. Just figure out how you're going to transport them before you agree to make them.
Of course, you could also use silicone muffin pans or individual silicone cupcake and muffin cups. They come in a variety of colors and some even have appendages on them for creating wonderful cupcake creatures. Silicone cupcake cups have lots of potential but please read my review on those before deciding to purchase them.
Cake Decorating Utensils:

I haven't found a big need yet to increase the number of spatulas I have, but having the 2 different sizes really helps.

I'm still trying to decide if this product is even worth the money or the hassle. I think if I can manage to get it work consistently, I would use it more often and really like it. The individual pieces kept sliding out of the holder or the pressure I used to create the design would cause pieces to retract into the holder (changing the design in the icing and making it uneven). One reviewer on the Wilton site suggested placing a large black clip on the holder to help keep the pieces in place. More testing and experimenting is required on this one. Update: I don't recommend this tool (I wound up giving mine away). I would instead recommend the Decorating Comb and/or the Decorating Triangle - the combined cost is LESS than the Icing Sculptor.
Featured cakes that use the Icing Sculptor are: "Fade In" Movie Script Cake
Decorating Tips - I have a variety of icing tips that I bought several years ago as a set. I've added a few more to the set since then as I needed them. Of course, if you get the icing tips, you'll probably want to also get the couplers and decorating bags as well. Wilton has a new TwistQuick™ Decorating Coupler available but I have not tried it out yet.

I have a set of brushes but usually only use 2 different sizes. If I were more of a painter, I'd go crazy painting beautiful patterns and pictures all over my cakes! The brushes I have are Wilton Decorating Brushes which have a painted wooden handle. I would prefer a set with plastic or acrylic (or even non-painted) handles because the paint on these tends to peel off after several washings.
Cake Icing Additives:

On occassion, I do use liquid food coloring, especially when I need a specific color that I don't have a gel color for. For instance, I used neon liquid food coloring for my Tiki Man Cake.

Application is easy. For a light shimmer, dust it on with a dry paint brush. For a more intense color with the shimmer, mix it with a bit of water, flavor extract or vodka. I've found you can wet the brush and then dip it into the Pearl Dust. I had a lot less waste that way.
Featured cakes that use Pearl Dust are: Electric Guitar Cake, Unicorn Cake, "Fade In" Movie Script Cake, Lego Mini-figure Cake, Kingdom Hearts 2 Keyblade Cake

You can purchase pre-made fondant or you can make your own.
Pre-made fondant is available in craft stores (Michaels, JoAnne's, Hobby Lobby, AC Moore, etc), at big box stores (Walmart, Target, etc) and online. It comes in many different colors and sometimes can be found pre-flavored. You can always purchase white fondant and then color and flavor it yourself.
You can also make your own fondant, called Marshmallow Fondant because it is made with lots of marshmallows. If you plan to make a cake using marshmallow fondant, be sure to read "Working With Marshmallow Fondant" which also includes the recipe I use for Marshmallow Fondant.
Featured cakes that use fondant are: Electric Guitar Cake, Unicorn Cake, Lego Mini-figure Cake, Kingdom Hearts 2 Keyblade Cake

The melting wafers come in a variety of colors and can be used whole (un-melted), melted and poured into molds or piped into lettering or made into Candy Clay for molding such as the head for the Baby Dragon Cake (The head was molded from candy clay and then covered in icing with the rest of the cake) or the burgers and hot dogs for the Grill Cake.
Featured cakes and cupcakes that use candy melting wafers are: Blue's Clues Cupcakes, Kitty Cat Cupcakes, Bumble Bee cupcakes, Bumble Bee Cake, Bridal Shower Mini Cupcakes, Cinderella Carriage Cake, Jack Skellington Cupcakes, Pikmin Cake, Baby Dragon Cake, Dragon Cake
Silver Dragees / Sugar Pearls: These little silver decorating balls, called silver dragees or sugar pearls, were used on the guitar cake. The Sugar Pearls, made by Wilton, are also available in gold and pearl colors.
I use dragees in moderation. Some brands are so hard they can be tough on your teeth.
Additional Add-Ons:
I try to use items that are easily found everywhere. Here is a list of additional things sometimes added to cakes:
- Popular candies such as Reese's miniatures, Tootsie Rolls, Twizzlers and jelly beans, Cinnamon Hots
- Chocolate Chips
- Marshmallows
- Rice Krispies (made into Rice Krispies Treats that can be molded into shapes)
- Fruit leather (Fruit Roll Ups)
- Graham Cracker Crumbs
- Silver Dragees and various sprinkles
- Cookies
- Pretzel Sticks
- Ice Cream Cones