Assuming you don't want to use gcc, you have several options:
VBCC (free, shell based, C/C99 only)
StormC3 (shipped free with devcd 2.1)
StormC4 (I think it's like 50 Euro now?)
SAS/C (if you can still get it)
If you are looking for a really easy to use IDE, stormc is good. It isn't the greatest compiler however but for quick jobs it is quite good.
Even now I sometimes use it to build a project that I will later compile with gcc or whatever.