There are epic weapons for everyone (right now priced at 25 seals, though that may change -- the weapons seem to be a little higher 5-man Heroic level), as well as blue boots, belts, gloves, and neckpieces for most classes and specs (all just 10 seals -- about equivalent to the Revered options the endgame reputations). Additionally, you can get tabards for each faction city (at 50 seals, that seems expensive, but they could have a special proc or ability granted with them), you can buy specially colored faction mounts for 100 seals, and at the top of the heap is an Argent Hippogryph for a whopping 250 seals. Seals, it seems, will also be able to be exchanged for reputation commendations, so if you just want to rep up with a certain old faction rep, you can do that, too.
Pretty enticing. We have yet to see how exactly seals will be earned or how easy they'll be to come by, but it seems like Blizzard is planning to make this a catch-all option for endgame in terms of picking up rep, mounts, or gear. Just like the champion tabards let us choose just how we could earn rep for the endgame factions, the Argent Tournament appears to be a chance for folks at level 80 to pick up whatever rep or options they like by doing whatever the Tourney offers.