If you plan on installing any themes or changing out lots of icons, I highly suggest you take a gander at some of these apps.

ShapeShifter, by the one and only Unsanity, is pretty much THE app you need if you want to install themes on your mac. It really is a must have and will only set you back $20. If you’re a tad weary of buying it, they also offer a trial of it. So you’ve really got nothing to lose.

So you’ve been using customized OS X themes for quite some time and think you’ve got a good idea for your own them? Then checkout ThemePark. It’s completely free and allows you to create themes that are compatible with ShapeShifter. It will even let you modify the interfaces of some of your favorite apps.

Panic’s CandyBar gives you the ability to control what icons are used for every item in OS X. It’s the safest way to play around with icons as it’s got a ‘reset’ option so you can always go back to the original should things get out of hand. With it’s simple drag-and-drop interface and $12.95 price tag, it’s a must-have and a steal!

Iconfactory’s IconBuilder is a filter for Photoshop and Fireworks that makes creating icons in the icon format a snap. IconBuilder basically lets you create any type of icon file for any system (OS X, Windows XP, Windows Vista, etc etc). This is a must have app for anybody serious about creating and distributing icons.