A big thank you to we Love You So for the pointer to the theme park maps collection, which in turn led to the pointer for Theme Park Brochures, which is exactly what you think it is — a collection of theme park brochures.
It’s available at http://www.themeparkbrochures.net/main.html.
I don’t have a count of the number of brochures here — several dozen? A hundred? The front page sorts the brochures both by date (there are a few that go back to the 50s) and alphabetically. Click on an item and you’ll get a page with links to scanned in parts of the brochure — this 1972 Opryland Brochure comes in eight parts so you can fully appreciate the groovy illustrations and ticket price list.
As We Love You So noted, there are other parts to this site, including the maps list (this one goes back to 1931!, link list (nice annotation), a substantial list of roller coaster builders and another one of roller coaster clubs (for coaster enthusiasts). Great browse.