Mac Tricks and Tips recently came out with a list of the Top 100 Essential Mac Applications, so I think I'll list my own essential apps (but not 100, sheesh!) that I use as Geek in Charge at CurrentMarketing.

1. Komodo Edit : If I'm not using vi as my text editor, I'm using this app. I could use any old plain text editor, but I'm addicted to syntax highlighting for code and hate working without it.
2. Fetch : I think the list from Mac Tricks and Tips is wrong about Cyberduck. I've had nothing but issues with it, and that's why I love Fetch as my FTP client.
3. Parallels : When needing to check a site across multiple browsers and multiple platforms, Parallels sure beats the pants off of a desk full of hardware. Gone are the days of 3-4 computers on or around my desk. Well, working ones that is -- I have a graveyard of dead towers behind me right now.
4. Spaces : Every Leopard install already has this, but if you don't have it enabled you should! I simply couldn't work as effeciently without it. I normally have my editors, terminals, Parallels, Photoshop, iTunes and numerous browsers all open at the same time. Without Spaces, I'd go mad (even before Leopard I used 3rd party apps to perform similar desktop magic).
5. iTunes : Okay, so this is a given. Every Mac-head out there has this favorite app, but as a developer it is very important to my work. How else could I stand banging out line after line of code if I couldn't fire up iTunes and listen to Green Day, Miles Davis, Led Zeppelin and Lady Sovereign (or a mix thereof) to blast in the background?

Well, those are the applications I wouldn't want to function without daily on my Mac. Now I'm going to go check out a lot of the apps mentioned in the Top 100. Which, by the way, is only a Top 99 -- Wallsaver is listed twice (47 and 58). It must be that good!