I think at one point, I owned every Babysitters' Club book, and most of the Sweet Valley ones. I don't really "miss" those...
I'll still reread L.J. Smith books though...like the Secret Circle, Dark Visions, and Forbidden Game trilogies, the Vampire Diaries books. oh! And Night of the Solstice and its sequel, Heart of Valor.
Lots of Christopher Pike and RL Stine when I was younger...my favorites were probably The Starlight Crystal (Pike) and the Fear Street Saga (Stine).
hmmm...what else... Shel Silverstein, I still like his poems

There was this one book, I think it's called Remember Me to Harold Square, by Paula Danziger...I must have checked that out of the library a thousand times.