If you are looking for a modern collectable then see if you can get your hands on a 22x. Nice gun and I would expect it to hold value well over the years. Besides that and some of the "special edition" stuff they sell now and then, your best bet is to look for the older stuff on the auction sites. Just be careful, some of the descriptions are very misleading. Personally, I buy guns that are uncommon and fun to shoot. Diana P5 Magnum, Hy-score 803, Older Crosman 2200 Magnum chrome version, etc.
Take care.
Russ S.