I've been using Code Crusader, a nice little "IDE," for quite a while. Although it's not really an IDE, considering it's a little ways away from what i consider being fully integrated, it
is a nice editor with support for generating makefiles, and with Code Medic, available seperately, you'll even have a debugger built in. Beyond that, they have some very interesting plans for future developments.
Other than Code Crusader, there's KDevelop, if you have KDE, but i haven't tried it. There are some other, proprietary IDEs, but i wouldn't invest in one of these unless you REALLY know that you want it. In general, i think there's a lot of free stuff that's just as good, if not better.
Oh, and if you want to go the *real* Linux way, there's always Emacs...
-Shelrem