More things for the IDE (Integrated Development Environment).  Xcode is the one I use for iPhone development,  so hint, hint Apple.

 Check Spelling Inside Comments
This a useful feature, really.  I often use the TextEdit application that came with my Mac and it will auto-correct while I type.  On average, this is a big plus when my fingers get a little out of order and transpose two letters.
Since the comments are about the written communication from one human developer to other human developers, having spell-check is really important.
See my previous posts that talk about having comments written in RTF so we can communicate with more than plain text.  (Why are we still stuck with plain-text source files in 2012?)