Warning: This is my recollection from about 1976.

[link|http://www.scottonline.com/info_NEW.asp|Scott] publishes books of stamp prices. [link|http://www.amazon.com/gp/product/0894873512/qid=1143317033/sr=2-2/ref=pd_bbs_b_2_2/104-2474938-6471904?s=books&v=glance&n=283155|E.g. the 2006 Catalog for the US and a few other countries]. They're generally retail numbers - you can expect to get at most 50% of that if you sell to a dealer.

There are similar books for [link|http://www.amazon.com/gp/product/0873499875/qid=1143317300/sr=1-4/ref=sr_1_4/104-2474938-6471904?s=books&v=glance&n=283155|coins], but I know less about them.

There are online places like the ones that [link|http://z.iwethey.org/forums/render/content/show?contentid=228059|Quirky was pointed to a while back], but I don't know if one is preferred above the others.

The money you get is for the collection is going to depend on supply and demand of whoever you deal with - don't take the book values as gospel. Ebay may be a godsend here. :-)

HTH a bit. Have fun!

Cheers,
Scott.