I have a Cavalry Arms lower and am very happy with it. Check out
[url]http://www.cavalryarms.com/[/url]
[url]http://www.cavalryarms.com/rifles.html[/url]
Also they have a section in the Industry area of this board.
This lower is made in one piece with the grip and stock. This contributes to the strength of the product. The plastic is very good. Their handguards, made from the same plastic, resists heat better than the milspec plastic. They have a picture of blasting away with Beta C mags and melting the gas tube, but not hurting the handguards, which had no heat shields installed. They do install heat shields on their handguards for sale.
These lowers (and they make all AR15/M16 furniture) come in various colors, too, black, OD, gray, brown, and some bright colors, blue, yellow, orange, purple. Check them out.