If you want genuine U.S.G.I.,
Fred's.
http://www.fredsm14stocks.com/
There's some real horror stories out there about dealing with Fred's (actually his dog's name). Some others have been lucky though. There are also export issues with the USGI M14 synthetic stock, of which Fred is COMPLETELY aware. He risks a very hefty fine if he's caught doing it without the paperwork, which costs more than you'll pay for the stock here. You may, or may not get it after sending payment.
If accuracy matters, and you want the best,
McMillan.
http://mcmfamily.com/mcmillan/
That or the JAE-100 stock.
If traditional is not your preference, or for so-called "tactical" stocks, you'll want to also look at the picatinny rail from
Ultimak (a replacement handguard that drops onto conventional stocks) and railed products from
Sage and
Vltor.