I got the Diablo 1/2 battle chest in mint condition guide book and all at the salvation army for $5 recently myself. Good finds.
As for other things I've gotten...in the last 2 or 3 trips(past month) to the 3 thrift stores I visit to pass time:
PC games, $1-2 each:
Riven(the sequel to Myst)
Alpha Centauri
Zoo Tycoon 2
the Diablo BC mentioned above
About 20 records for $1-2/each, I don't feel like listing them all. One of them is a glorious christian cold war propaganda record but I can't go into any more detail because of forum rules, the others are mostly jazz records.
Banjo Kazooie for the N64 $1
Oh yea, the post below me reminded me that I found a $700 coat(priced at a store that was literally 2 minutes away) for $20 a couple months ago. That's worth mentioning above the usual $1-2 things..
It even fit me. I have very odd dimensions(HUGE shoulders) so I usually just ignore clothes in thrift stores. It caught my eye though and I was extremely happy when I could actually wear it. Just had to have the buttons repaired and had to get it dry cleaned.
Now I just need a place to wear it because it never gets cold here and I'm hot natured anyway..