Black Books is awesome. Though it wasn't BBC, it was Channel 4 -- a nascent *gasp!* commercial station, with commercials. (The only good shows are on the commercial channels... yet you're still expected to pay the annual TV license fee... this is why we watch DVDs)
If you like Black Books, you should check out Spaced as well. Simon "Shaun of the Dead" Pegg's big break and very funny.