GG&G
http://www.gggaz.com/index.php?id=112&parents=60,63
I have several and they are a nice addition...
Of course, there are some here that would likely say you were wasting your money because the M4 already comes from the factory with a bolt handle...
I don't have personal knowledge, but I guess $25.00 does put a sizeable dent in a double-wide payment...