Mac only: Somewhat like a mix of Quicksilver and the Terminal, DTerm launches with a keyboard shortcut, automatically integrating your working directory and selected files, so you can spend less time typing and more time running commands.
If you find yourself working with the Terminal often, it can get annoying to constantly run the same commands, type out full file names and work completely independent of your working application. Sure there are tools out there like previously mentioned OpenTerminal, and you can always drag and drop files into the Terminal, but even that gets old quickly. Why do that when you could just select the files in the Finder, hit a hotkey and have DTerm automatically cd into your that directory with the selected files' paths ready to be pasted into a command?
DTerm integrates with a ton of apps and will even open a new Terminal session for you if you have more commands to execute. You can quickly paste in the last command's results, add the selection from any app to your command and do lots of other formerly tedious tasks with quick shortcuts. Sure it may not make you feel like you're in the Matrix with that big plain text display, but if you're sick of copying and pasting all the time, DTerm is sure to save you a few steps when you need to run some Unix commands. Hit the link for more information, as well as a cool demonstration video.
DTerm is a free download, Mac OS X only.