I love Evil Black Rifles. I really do. They make GFWs nervous (if you're lucky, they make them void their bladders). EgregiousCharles, writing on Geek With A .45's blog, has an interesting take on my personal favorite, the HK-91 and it's clones.
I like the HK. Tough, reliable and simple, it packs a considerable wallop with it's 7.62x51 round. Ammo is still fairly cheap, and as Charles notes, magazine are available for basically dirt cheap.
And when you can get a JLD PTR-91 for $595 (see the article for details), well, I can buy two, a hundred magazines and a thousand rounds of ammo for what an M1A will set me back. That's a lot to love, in my book.