[felxh]

7) +1 Spotlight or Quicksilver if you prefer. There is also Alfred http://www.alfredapp.com/

If you listen to music while working, I also find Coversutra http://www.sophiestication.com/coversutra/ or Bowtie http://bowtieapp.com/ very useful.

[maximilian]

Google has a new launcher that I think is developed by the dude who made quicksilver (who now works at google afaik)

http://code.google.com/p/qsb-mac/

[tta]

There's also LaunchBar. http://www.obdev.at/products/launchbar/index.html

[mmorris]

+1 for Launchbar.

After going back and forth between Quicksilver and Launchbar for a while, I eventually settled on Launchbar because I found it to be a bit faster. I think Quicksilver is more powerful, but I never really used the additional capabilities so it ended up being a pretty easy choice for me.

Even after Spotlight was added to OS X, I stuck with Launchbar because it takes a few less keystrokes for many tasks and it has search templates (so searching Google, a dictionary, or a thesaurus requires only a few keystrokes). Quicksilver can also do something similar, I'm not sure about the other options.