Samuel Cohen over at theappleblog has a nice post up on ten top apps for laptop-toting Mac users. Many of his selections are old favorites (Quicksilver), but there are a few here that are new to me. The CornerClick Preference Pane allows you to assign various actions to the corners of your screen. According to Sam, fKeys lets you "remap the enter key (not the return key. The enter key. It's the one that's in between the command key and the arrow keys on the right-hand side of your laptop keyboard) to an option key, just like on a full-size keyboard." Finally, Noise is a simple app for generating pink noise for when you want to tune out the Muzak at your local coffee house. Check out the original post for the rest, while I go play with CornerClick.
[Edit: Corrected CornerClick description; thanks Dan. I was probably thinking of the replacement trackpad driver SideTrack which does allow for assigning functions to corner clicks on the trackpad].