TextMate is my prefered text editor on OSX, it manages to be the simple whilst doing lots of cool things. For a cross-platform choice used to use jEdit. Aptana(/Ecplise) is probably the most popular IDE across OSX and Windows.
These days I tend to use MacPorts to install my dev environment, it matches a linux hosting box much more easily and can install other packages, although it is still slow to install.
I’m not a graphics person really, I generally just need something for editing pictures and graphics for web use, I don’t really ‘create’ graphics as such. Graphics Converter seems to fit the bill, although it isn’t free, it has good export options and easy cropping tools. Another option is ImageWell.
iPhoto is pretty good for being you’re picture library, although I may look into Apature (>=2) at some stage.
SVN seems to be baked into Leopard, so if you’re happy with the command line, that will do you. For a graphical SVN tool I use Cornerstone.
Omnigraffle is something I’ve heard of several times in references to creating IA diagrams, a Mac enhanced version of Visio if you like.
macromedia studio is also available for the Mac.