Email and instant messaging do not work well for sharing code. They don't preserve whitespace, the fonts aren't monospaced, the spell check gets in the way, etc.
Paste bins are better, but they are too static if you're looking for collaboration. Also they don't have a good editor, they're only good for copy and paste.
Collabedit has what you need - a good editor, syntax highlighting, real-time collaboration, chat and versioning.