I love Redhurst, but damned if I can figure out how to run a traditional D&D game using what's essentially Hogwarts. It's a great home base for wizard characters, though, and would work as a place to be from between semesters.
More practical is Ptolus, which has everything one needs to run more than one 1-20 campaign in a fantasy metropolis. You can do a campaign of nothing but dungeoncrawling (pretty much every Goodman Game DCC module can be shoved into or under the city with no real effort -- change "kobold" to "ratling" half the time and "Old Gods" to "Galchutt" and you're done!), an epic campaign to save the world (and arguably the multiverse) or just one set in the intrigues of the city, whether among the nobility, the looming civil war or among rival criminal gangs. It's also got a good number of previously published works from Monte Cook through Malhavoc and other publishers (including some of the Book of Vile Darkness content from WotC) that fits into the setting, giving you even more to do.
Well-supported is the first edition of Freeport, which has modules, PDFs (many by quite well-known designers) and supplements. It's a good time to pick it all up, because Green Ronin is about to jump the setting forward five years in 2007, so if you get the old stuff, you'll have enough for years worth of play when the new stuff hits, too.