The first announced games include Wing Commander Privateer, Dungeon Keeper, and pioneering first-person RPGs Ultima Underworld 1 and 2. And those three are available right now for $5.99 each! Three more EA classics" are coming before the end of June, and then "over 20" more games from the publisher are coming this summer.
Unfortunately, System Shock and Syndicate aren't part of the agreement right now, due to rights issues. But, a GOG spokesman said, "never say never."