I always think they leave out some every time, so I will now give you my own list...
1. Quicksilver - Almost every list I see has Quicksilver on it somewhere. I agree completely. However I will note to first time users, it took me two installs (a month apart) and a week before I really got the hang of the program. But now that I know the basics I learn something new about Quicksilver almost every day.
2. AppTrap - People will tell you that all you have to do to uninstall applications is to drag them to the trash. That is true, mostly. That tip forgets the receipts that are installed with every program in a receipts folder in the Library. While there are other applications that delete applications completely, AppTrap is a Preference Pane. When you drag an Application a box will pop up and tell you, "You are moving an application to the trash, do you want to move its associated system files too?" This application beats all the other options I've found.
3. Service Scrubber - Under the Application name menu (upper left-hand corner of your screen) is a list of services. That, more than likely, you will never use. Service Scrubber lets you remove the ones you don't want (or, in my case, all of them).
4. Shades - Ever use your Mac at night or in a dark room? Upset that you can't turn down the screen brightness as much as you want? Be upset no more. Introducing, Shades. Turn your screen down ass much as you want (please not to far or you'll go blind).
5. Switch - I use this program so much I wish I had money to donate to the programmer. Switch converts from almost any audio format to mp3, and a couple others but I can't remember what they are because I don't use them. Switch does it fast and can also do batch requests. (Please note that the product page wants you to buy the application. But if you look hard enough you'll notice the free link. Just in case here is the direct download link http://www.nch.com.au/switch/switchmac.zip)
6. FireFox - It's fast, customizable and just works.
7. Handbreak - Every time I see someone mentioning DVD ripping software (that's not Handbreak) I want to bang my head against a wall. Handbreak is the fastest, simplest, most customizable DVD ripper I have seen. Hands down.
8. Gimp - Photoshop, but not. It does almost everything Photoshop does, looks good and is Open Source. What more could you ask for? (There's even Gimpshop. Gimp that looks like Photoshop so you can use it easily.)
Ok. That's my list. Please note, everything on this list is free.
These are the things that I, as a video editor/student/graphic designer/gamer, use all the time.