I use TextMate, too, and complete it with TextWrangler which helps me with line feed issues, not ideal, though, still looking for a good solution to control line feeds and encoding (of projects with loads of files), I miss my Scite from Windows
Further :
Terminal (included), the ditto command to merge folders
Renamer4Mac (bought) to rename
MAMP (free version) as server, with XAMP I can’y get the mail server going
FileZilla for FTP, more out of nostalgic reasons, could import my servers from the Windows version, though
Versions (bought) for svn control
FileMerge (included) to compare files / projects, You need to have
GraphicConverter (use the trial) for favicons
Dashboard 3D LookUp with GoogleEarth (free) for some nice route maps
iChm (free) to view the PHP manual, but the search is poor
iPhoney to view the mobile sites
Jing for the tutorials
VirtualBox to check IE
RegExplorer to test RegExs
For basic testing I switched to Safari, much faster and comfortable than FireFox, especially Safari’s cache handling is smoother, got even a shortcut to purge, took some time until I stumbled over ‘Show the Develop menu’ in the preferences)