Beach Boys
Only one I've got is Pet Sounds, but what a damn fine album it is. Usually regarded as one of the best of all time. If you're looking for all their surfing singles, you'd probably be better served picking up one of their countless greatest hits compilations, though--you'll find none of them on Pet Sounds. It's got a really mature, layered sound compared to their earlier stuff.
Bob Dylan
My personal favorite is Blood on the Tracks, but it looks like you've already got that one covered. You can't really go wrong with anything he did in the sixties, though--Blonde on Blonde, Highway 61 Revisited, Another Side of Bob Dylan, Bringing It All Back Home. . . Just pick one. They're all good. John Wesley Harding and Nashville Skyline are also good, but a little more country-tinged than the others.
Pearl Jam
Ten is their most-successful record, commercially, and it's also the only one that lazy John Q. Public says was any good, and that "everything they've done since has sucked." (Don't listen to him.) Vs. is good, Vitalogy is good, No Code is good (and has kind of developed into a fan favorite--after some pretty poor reviews when it first came out), Yield is good (and is probably my favorite of theirs), and Riot Act is good, too. And their new record, Pearl Jam, coming out in May, sounds like it could be promising, too. But, whatever you do, stay far, far away from Binaural. Good Lord, that's an awful record.
Prince
Purple Rain and Sign 'O' the Times. But almost all of his eighties output was nearly just as good--Controversy, Dirty Mind, and 1999 (all before Purple Rain). And I really like Parade and Lovesexy, too (both bookended Sign 'O' the Times). But Purple Rain is great--nearly every cut made the radio that year, and one of the only ones that didn't is single-handedly responsible for those annoying little "parental advisory" stickers that you don't see at Wal-Mart. . .
Smashing Pumpkins
Siamese Dream. If Mellon Collie was just a single-disc (instead of being a bloated double-album), I'd probably say that, but it's not, so I gotta go with SD. It's got a really great, thick-ass guitar sound, and Jimmy Chamberlin's drumming is some of the best around. The intensity kind of tapers off toward the end, but there's really not a bad track in the bunch.
Wilco
I'd probably say pick from Being There, Summerteeth, or Yankee Hotel Foxtrot, depending on your tastes. Being There (folky), Summerteeth (poppy), or YHF (music-y). A.M. is the least-interesting of their work, and A Ghost is Born is. . . well, it's A Ghost is Born. Hard to classify. It's a lot better live than it is on CD.
(I had originally written a lot more here, but it was too wordy and boring, even for me.)
