A bunch depending on what you are willing to pay:
DD Ross
Badger Ordnance (M4)
Dakota
Pacific Tool & Gauge has the regular OEM clone and the Oberndorf model
Other than PT&G's offerings, I find the other companies charge ridiculous amounts for their BDLs. That being said, I found a great deal on a Badger M4 (Here on the 'Hide) and it is a great piece of kit. Fit and finish are A+. Also, I use Timney triggers and find the wide guard of the Badger more fitting. On a OEM Rem BDL the Timney is as wide as the guard. However, the Badger is very hard to open. The lever is subtle and has a strong spring making it difficult to simply push it. I happen to like this feature as it guarantees no accidental openings, but I know it bothers others.
I've had both the Regular and Oberndorf PT&G's as well and they are also well made. The Aluminum versions way next to nothing and are a great option for light weight builds. I would go with one of these as the quality is as good as anything else, but the price is better.