The David Rumsey Historical Map Collection is open to the public online. He's got a personal collection of many, many maps and he's had over 20,000 of them digitized for your easy inspection. He specializes, but is not limited to, 18th and 19th century North and South America. The search box for "Texas" retrieves 1,200. I took the pleasure of surveying the Tanner map to check how Coahuila related to San Antonio. The image was sharp and clean.
It's not surprise that he received a special award for his collection and public space from the Special Libraries Association.Of course, he sells reproductions.
Check him at http://www.davidrumsey.com/