I took the first trip to my FLGS in the past three months and noticed that since I was last there they had a bunch of second-hand shadowrun books for about AU$25 each ( i think that's just under US$20).
As much as I would have liked to buy most of them, I'm a bit short on funds at the moment, so I only got universal brotherhood, as it looked awesome and it's supposedly rare.
Unfortunately I can't remember most of the books they had there, but which ones should I make it a priority to pick up if I find?

Secondly, Did Sr1 and Sr2 have limited edition releases like Sr3 and Sr4 and if so, how much do each of the limited editions generally go for?

For both SR1 and SR2, the closest thing to a limited edition would be if you were to find either book in hardcover, instead of in paperback. The covers were the same. There was no numbering. However, the hardcovers were a bit rarer. Honestly, though, I think neither hardcover were anywhere near as rare as the SR4 and SR4 LE's.

As far as rarer books go -- your best bet is to check eBay. I think the "most valuable" books, aside from UB, are the Lone Star and Corporate Security books. But, there's a huge variation.

Yeah, Sr3 released a 1000 copy run in hard cover as well. The BABY. We all want one to go with the rest of our limited collections. =p

Make sure that your copy of UB has the fiction insert. If it doesn't, you got ripped off; That was the best part.

I still think Mercurial was great. And Harlequin, if you can forgive some glaring errors in light of a great run. Oh, and Seattle Sourcebook, if just for the glossy photos. Kitschy goodness.

Fiction insert, do you mean the large section bound on the top with the front cover advertising the universal brotherhood? Isn't that most of the book?

UB consisted of a loose cover, a top-spined fiction booklet, and the adventure Missing Blood. Make sure you have all three.

THe rarest of the mainstream SR products is probably Sprawl Maps, followed by the DMZ. The rarest book (aside from the limited editions) would be Prime Runners, the Lonestar Sourcebook, and the original 1st edition-only-rules Street Samurai Catalogue. The first two vary quite a bit in availability, but seem to be pretty consistently rare.

Paranormal Animals Of Europe, LoneStar Sb and London Sb had become the three rarest books, at least here in germany.

I do not see too many Atzlan books. AH is right about the map pack, not to be confused with the readily findable Sprawl Sites (though an excellent book).

Another book I don't see too often is Corporate Punishment.

Got that one. Same with UB and Bug City.

I'm still working on Lone Star...

ok i have to ask because i couldn't find anything on them...
what is BABY and UB???

UB = Universal Brotherhood.

BABY is (from what I'm gathering) the limited release version of the SR3 corebook.

A fantastic combination of rarity and total and complete bitchin-ness can be found with the Lone Star Sourcebook. I paid around fifty bucks US for my copy. It's that good.

And no it's not wrong to have books sitting around. MUST....HOARD....OUT of PRINT....BoOkS>>.......erk....