Ack, been too long! Surely other cool freeware/shareware has come out!
Ones that I find essential are:
- Synergy
- iTunes remote in the menu bar, along with a cute 'MTV' style bar that shows the current track. Easily worth the 5 bucks.
- Safari Menu
- Puts all my Safari bookmarks in the menu bar. I found a different one that could also launch applications and files, but the interface sucked. 
- resexcellence hacks
------> Specifically:
--------------> *Safari Tab 2, Safari Tab Highlight & Safari Fire Progress from here
AND this ->
as my boot image
- LiteSwitchX
- Basically cooler Alt-tabbing feature
- MenuMeters
- Shows a bunch of stats in the menu bar. I only use the processor usage one. I don't really use it, but it's fun to watch.
- Tinkertool
- Does a whole bunch of cools stuff with the preferences. Definately worth the d/l.
- WindowshadeX
- Allows windows to roll up, become transparent, or be minimized in an awesome way you can't believe until you see. Brings back a feature Apple shouldn't have cut. 
- Sophos Anti-Virus
- I'm not very impressed with this program at all. Luckily, I got the free demo version first. I'm merely waiting for my real virus protection proggy to get in from eBay.
- Acquisition
- I love this P2P program. It has the number of Limewire, only it works.
- Geneforge 2
- I played the demo for both 1 and 2 of this game. I always get stuck, become frustrated, and quit out of anger. It's a great game though, if graphics don't matter to you.
- Glider Pro
- The author just distributed this game for free. I'm awful at it, but it was incredibly fun back in it's heyday, and it's just as fun now.
- Periodic Table X
- Heh. To tell the truth I haven't used this program once. I figured I'd need it for college though. I'm sure there is a better one out there that is freeware though, so I'll be searching for a new one soon.
- ClearDock
- It made my dock a neato lime green with a blue outline. You can't get cooler than that!
Phew, I think those are the only ones I use. For the record, all the red words are links to the product's page, and all were hand copy/pasted and all that. This post has taken almost twenty minutes. So ever if you hate Macs or these programs, click one so I don't feel like it was all a waste. :P
Hopefully there are other Mac fiends out there with just as fun apps.
Don't be shy!