I would definitely check out the AT cks77 mentioned above but I can also vouch for the Hisoundaudio POPO as I own them.
I received them as a review sample from Hisoundaudio and at first I didn't like them but they grew on me. The bass is fantastic, hard hitting, full of body, and sub-bass is one of the best I've heard on a sub-100 IEM if not the best. Sadly, the bass does overwhelm the mids and highs a little so it becomes a very bottom-oriented sound and quite warm as well.
As a person who listens to a little dubstep, I love the bass that the POPO IEMs can produce but dubstep also has screeches into the highs as well and that's where the POPO IEMs disappoint a little in my opinion (granted I was listening to the Triple Fis previously). I also thought the soundstage could be a bit wider but it's not bad at all.
You can get them around $60 on ebay (I'm pretty sure Hisoundaudio has their own shop on eBay as well) but here's one link: