Replica Omega Seamasters are relatively common.  They come in a variety of grades, from poor Asian trash, to high quality ETA-based models.  With Omegas it pays to know what you're looking for.  Many fake Omegas have inaccurate backs or dials.  They may 'look' good, but any Omega buff would spot these flaws early.

OMEGA Seamaster

Compare to Genuine Omega Seamasters on eBay

Omega 1960's Seamaster 300 Automatic Steel Men's Watch US $858.00 (20 Bids) Auction Ends: End Date: Thursday Sep-02-2010 15:43:59 PDT Add to watch list

Vintage OMEGA SEAMASTER, DAY/DATE WHEELS, SS/18k inlay US $600.00 Auction Ends: End Date: Thursday Sep-02-2010 15:49:18 PDT Add to watch list

OMEGA SEAMASTER Vintage Mens 18K Yellow Gold Watch US $2,300.00 Auction Ends: End Date: Thursday Sep-02-2010 16:05:08 PDT Add to watch list

VINTAGE OMEGA SEAMASTER LADIES WRISTWATCH WATCH! US $495.95 Auction Ends: End Date: Thursday Sep-02-2010 16:05:32 PDT Add to watch list