Nice find, Silver Moon! In the age of ebay, where EVERYTHING is considered collectible and valuable by everybody, it's pretty rare to stumble onto bargains like that.
I don't have time to post my whole list. A lot of the stuff has already been mentioned.
But I did want to add my voice to the chorus praising Tact-Tiles. Without a doubt, these things are the single most useful game innovation I've ever incorporated into my game, ever.
I simply cannot see myself ever going back to the vinyl battle mats. Wet erase? Are you joking?
An excellent, excellent product worthy of consideration by all DMs.
1E PHB, MM, and DMG - I have spent untold hours using themand still use these today after 20 years.
Traveller little black books - still play with these over all other versions of Traveller
Vampire: the Masquerade - Weekly game that has been going on for ~10 years
Magic the Gathering legends cards - spent two years playing the game and then sold them all for enough money to pay back my investment and pay for a semester of college.