Jason Alexander has a great post about must-have mac apps and some of the settings that he uses. I am in a similar boat as Jason, being primarily a .NET developer and former Windows user who has switched to the Mac I get tons of questions about what apps to use and how I like it. I thought I would go ahead and lay out some of my must-have apps and tips here:
My must-have apps for the Mac:
1) FireFox and Camino: I agree with Jason here, I couldn't get into Safari. I like Camino, but the various plugins I have become accustomed to keep bringing me back to Firefox. (Firebug, Del.icio.us, Google Toolbar, Alexa, etc)
2) Adium - Again, I am with Jason here. This is the best messenger app I have ever used on any platform.
3) Ecto - It's what I am writing this post in. Great blog posting tool that wasn't too expensive and does a great job.
4) VMWare Fusion - I have never used Parallels so I can't compare the two, but I loved VMWare on Windows and I love it on the Mac.
5) Quicksillver - It really is as cool as they say. Great launcher app with all kinds of neat features.
6) TextMate - Again, it's as cool as they say. Not only am I using it for Rails development I am using it for all of my text editor needs.
7) Cyberduck - Good little FTP program. I am thinking about buying Transmit, but I have bought enough Mac software this year already.
8) svnX - This is what I have been using for SVN access, there is a finder plugin as well like TortoiseSVN but I couldn't get it working with the latest version of Subversion.
9) Twitterific - The twitter client that all the Windows people lust over, been a little weird since Leopard but hoping a new release is coming out to fix the issues.
10) delibar - Toolbar app that gives me easy access to all my del.icio.us links.
11) Fan Control 1.2 - I like this one a little better than smcFanControl since it lets you set temperature thresholds. These things run hot.
12) Transmission - Free BitTorrent utility that I only use to download legit stuff.
13) Writeroom - One of those cool word processor apps that blacks out the rest of the screen and makes it feel like a typewriter, it's great if you want to focus on something.
14) CocoaMySql - A nice little MySQL client.
15) Flip4Mac - Play VMW and WMA in Quicktime
16) Growl - Toast for Macs
I have been trying out CSSEdit which is a nice looking CSS editor as well as iWork.
As for configuration tips I have a couple small ones, but make sure you read Jason's.... I do just about all the same things.
1) I setup my Active Corners a little bit differently than Jason. I put All Windows in the top left, Dashboard in the top right, Desktop in the bottom left, and Space in the bottom right.
2) Under System & Preferences -> Keyboard check the "Use all F1, F2, etc. keys as standard function keys". Using Visual Studio and hitting Fn + F5, Fn + F11, Fn + 11 is a pain.
A couple of accessories I have picked up too:
1) I picked up a Lapinator. Did I mention these run hot?
2) Option GT Max 3.6 Express - Don't believe the guy at the store who tells you it only works for Windows.
3) Brethaven Edge II - Great small case, not much room for anything else. But the extra power adapter pouch helps.
Well, that's about it.
-James

Wow, great. Now I just need to actually get my first Mac! :)
What about personal finance? I've been a die hard MS Money user for over 5 years now and I'd hate to have to fire up a Windows VM on my Mac just to do finances.
Any good Mac apps in the finance space? Particularly ones that can automatically sync and balance accounts with the major online banks like MS Money does?
Joey,
I have been using Microsoft Money on my server, I only have it over there so both my wife and I can access it. I have heard good things about Quicken on the Mac though.
Thanks for the tip on the Lapinator.
Nice list. Yeah, the lapinator looks good. I made my own with plywood and pipe insulation...not as slim, but it works. I've found iusethis.com for a source of popular apps and such. Off the top of my list would be the Unsanity products HERE, of course, as you've listed it already, Flip4Mac, and a few other good ones, iBackup, info.xhead, and another one by the Flip4Mac people, Drive In