TextExpander (mac) – You can set up customized abbreviations for frequently-used text strings and images. It also auto-corrects selected words that I type incorrectly all the time. It’s better than spellcheck, it’s typefix.
PathFinder (mac) – Does everything Finder does and a zillion other things. It’s one of those apps that I find some trick new feature every week or two.
XYPlorer (windows) – Like Pathfinder for mac, it does everything the system file explorer does with loads of additional convenience features built in. This one has great options for batch file renaming and mp3 tagging (among many other features).
Sizer (windows) – Sizer lets you resize any window to an exact size and position with a right-click on the top of the window. You set up the sizes and positions you want in the prefs. I want this for mac more than anything, but haven’t found it yet..

Textmate – I’m a former PC user turned Apple lover and have found textmate to be possibly the OS X response to Ultraedit on windows.

Cyberduck FTP – Sure there is Fetch but cyberduck happens to have built in support for textmate (since textmate doesn’t have a built in FTP Client). Easy to use, fast to upload what else could I ask for?

And lastly Docks.. It allows me to choose different docks for different things, I have my work dock full of all the apps I use for work, a dock I use for programming … You get the idea..

Unfortunately two out of the three programs I listed are shareware.