Fawlty Towers cover art, courtesy of the iTunes Store
Over Thanksgiving weekend, I noticed that the iTunes Store has Fawlty Towers (iTunes, IMDB, Wikipedia) available for purchase. Each season was $9.99 at the time, they're now just $1.99/episode (ie, no discount for buying the season at once).
Only twelve episodes were made, for better or for worse. It's some of British comedy's best, and even at $12 a season, it's a good deal. (The cheapest I could find the DVDs is $20 a season.)