I've done this a lot. My TV on DVD collecting has gotten a bit out of hand and my wife keeps asking "Are there any more shows you HAVE TO have?"
I have everything so far released for X-Files, Buffy the Vampire Slayer, The Simpsons, Futurama, South Park, King of Queens, MST 3K, Monty Python's Flying Circus, The Ben Stiller Show, and I just recently got the Special Edition set of Freaks and Geeks (only available from the show's official website. It's more expensive, but has much more for diehard fans of the show. I HIGHLY recommend it)
Season One of Monk is coming in June, along with Season Four of The Simpsons, and Season One for Reno 911. I'll be getting them all, along with Season Six of Buffy in May. And I preordered NewsRadio Season 1 & 2, but it's been delayed while they add more content than just the episodes.