[mtsr]

I've always used ii, jj and kk, etc. These are just as easy, but allow languages/editors without variable renaming to do a useful search/replace on them, because you just know you will at some point.

[jstimpfle]

Most editors have at least regex search / replace. Most regex flavours allow you to do '\<i\>' or similar to specifiy word boundaries.

[mettamage]

Thanks for this tip, would never read it anywhere else and gave a small boost in productivity.