Although you can already get a crapload of Pearl Jam songs in "Rock Band" (including the entire album, "Ten"), there's still more coming your way in July, thanks to a track pack. The pack will include "Brother," a live version of "Alive" (natch) and a live version of "State of Love and Trust." It'll run you 2 bucks if you buy each song separately, or $5.50 if you pick up the bulk of 'em.
It's pretty interesting that "Rock Band" is staying away from the band-centric releases that have done rather well with the "Guitar Hero" franchise. Apart from "The Beatles: Rock Band," they're really not going that route, instead opting to release massive track packs rather than full-on games (see: "AC/DC Live"). Will the floodgates open after "The Beatles" drops? We shall see in September.