cscope can be installed via
MacPorts.
MacOS X comes with the BSD version of ctags. You can install Exuberant Ctags, which you're probably more familiar with, from MacPorts as well.
Most coding is done in Objective-C using XCode on Mac OS X. XCode also supports C and C++ development as well.
There's also
Eclipse or
Netbeans.
If you don't want a full on IDE, there's
Text Wrangler, which is pretty popular with programmers.
Personally I use
TextMate, when I'm not using MacVim (also installable via MacPorts). If you're from the Emacs school, there's
Aquamacs. Or course, Terminal versions of both vim and emacs are preinstalled.