Building up your collection of cake decorating tools is almost as fun as it is to actually decorate a cake! There are thousands of different gadgets and gizmos out there, but only a few are really necessary. My suggestion is to start with the basics and then grow your collection only as you need the tools. Doing it this way will save you some money upfront, and get you the essentials that you will need to begin decorating beautiful cakes right away.
The most essential tools for baking are the cake pans themselves. There are hundreds of thousands of different choices out there, but only a few are actually necessary to have in your cupboard at all times. The most basic is the round springform pan. It's smart to have at least three different sizes of these so that you can create tiered cakes (with or without the stands). Generally, the three sizes to have are 9", 11", and 13" inch. You can increase the height of any tiered cake by baking another cake of the same size and stacking it on top. It's also wise to have a set of square and rectangle cake pans in roughly the same size as the round ones. The best place to buy shaped cake pans is online, since they tend to be pretty expensive at kitchen supply stores.
The other essential tools are a set of smooth spatulas. I keep a small, medium, and large spatula on hand. Cake edgers are also important so that you can texture the sides of your cakes. Don't go crazy buying up all edgers you can find, there are so many that you should only get them as you need them. Also, keep a set of icing tips with lots of extra bags. Like edgers, tips should be purchased as you need them, unless you can find a large set at a great price.
Baking is fun and helps bring families closer. Having the appropriate tools at your disposal will help you be more motivated to bake, therefore doing it more often.