Every time someone gets a mac I get a phone call or an email asking what software they should install. As a resource to those folks I'm putting together a list of software I use every day. This is not necessarily a list of the best pieces of software just the software I use and like. It's not all free, but it all makes me happy. I hope to update this as time goes on. I'll also post a list of software I use less frequently soon.
Quantrix (http://www.quantrix.com/) - Had to start with something that wasn't on anyone else's list.I was turned on to this recently by a co-worker and it has replaced excel. It's not just a spreadsheet, it's a modeling package. The professional version has the ability to work with databases through ODBC/JDBC. It's not just a 2D design but far more data centric. Very much an easier to use Mathematica.
Parallels (http://www.parallels.com) - Need to run Windows software on the same box? This is the way to go. For the last 10 months I've been doing Windows development on my Mac running .NET's development environment under parallels and it's been smoother than running under just windows. It seems that among other things OS X makes a good poor man's firewall.
MS-Office (http://www.microsoft.com) - Currently the best office product for OS X. To put that into perspective, I loathe Office for Windows and really like working with the OS X version. It feels natural and like it's part of the OS.
TextMate (http://www.macromates.com/) - A solid programming editor for OS X. I like a good solid programs editor and this one is my favorite.
Firefox (http://www.mozilla.com) - Yes, I know Safari is there, but I prefer Firefox, probably the unwashed hippy linux user deep down inside.
Adium (http://www.adiumx.com/) - An IM client which is a port of GAIM to OS X. Provides access to AIM, MSN, Jabber, Yahoo, G-Talk, Bonjour, Lotus Sametime, Novel Groupwise, Gadu-Gadu, Live Journal, among others. I'm hoping that next there'll be a direct twitter interface (hmmm, maybe I should write that).
Twitterific (http://iconfactory.com/software/twitterrific) - A brilliant, simply brilliant Twitter client.
Transmit (http://www.panic.com/transmit/) - A nice FTP product that exposes all necessary functionality to automator, which is nice when building workflows. Can't recommend it enough.