There are too many potential combinations to search for them all. I'll just cross my fingers and hope this isn't an all too familiar topic.
What older comics are you DYING to see collected into a trade paperback or hardcover?
Which were you pleased (and maybe even surprised) to see collected?
I'm not sure this fits the working definition of "classic," but the first that springs to-mind is the Perez-era Teen Titans tales. I've seen WHO IS DONNA TROY (which I repeatedly get mixed up with the more recent "No, really. Who the hell IS she?!" or whatever it was called), the TRIGON story, and the Terra/Tara one (Judas Contract or something).
I'd almost given up hoping that this would happen. I'd never (and still haven't) read these stories in their entirety. The DONNA TROY one wasn't on my list, but I'm kinda curious. If nothing else, I'm sure it's purdy.
The Trigon and Tara stuff, though... I've been aching to see these collected. Searching for comics can be kinda fun, but finding them can be a bit of a letdown if the stories aren't great, the images have degraded, or if that glue-like funk stinks up the place.
From what I've seen, this stuff is just what the Dork Doctor ordered. I've gotten one, so far. I hope to get the others after I've read a few more of the books I recently purchased at a 'Con.