TEXbooks (née TEXbook) was created in 1995 by me (Emery Berger, now a professor at the University of Massachusetts, then a Ph.D. student at UT-Austin). There was no web-based book exchange at UT, so I wrote one. The goal was to take full advantage of the Web to make it easy to buy and sell used textbooks (thus avoiding getting ripped off by the campus bookstore). TEXbooks was the first book service anywhere to provide e-mail notification when a book you want arrives. It also features a very carefully-designed user-friendly interface.
At the time, the Texas Union Business Interests (née "Finance") Committee was operating a paper-based book exchange service. I approached them and they decided to adopt TEXbooks instead, making it the only official UT textbook exchange.
At its peak, TEXbooks has had over 2,000 books posted for sale, making it not only the first (and only official) UT book exchange site but also the largest. At the beginning of the fall and spring semesters, it receives hundreds of hits per day; since April 25, 1998 alone, it has received almost 90,000 hits. The traffic on TEXbooks grows by leaps and bounds every semester; its listings on UT Web Central and Yahoo!, along with Texas Union advertising and some Daily Texan coverage, have helped build awareness and use of the site. TEXbooks now has a new address, TEXbooks.com, which should make it even easier for people to find.
In case you're curious, TEXbooks is written in Perl. Like Winston Churchill said about democracy, it's the worst scripting language, except for all the others that have been tried. (Although if I were to do it over again, I'd probably use Python instead...)