Get a Netflix account and buy yourself one of these Blu-ray players that will access your Netflix streaming stuff. Then you can watch TONS of TV series in their entirety at no additional cost. I know this is not exactly what you asked but it is by far the easiest way I've found to sample things without having to buy all the DVDs.
You can also stream netflix through an xbox 360 if you have it hooked up to a connection or have the wireless adapter. I'm not sure if you can on the PS3 which HAS a blu-Ray player already. Ha, I don't game-I know people who love electronics.
Fully agree on Weeds. I'm borderline addicted. It's Desperate Housewives (or dispicable housewives as my mother calls them) but with thugs and drugs. Riveting.
Even though you've named network-only shows, since others are chiming in with cable titles:
Six Feet Under - Incredible series, sometimes uncomfortable & cringe worthy but SO worth the time.
The Shield - Not everybody's taste, pretty disturbing at many points but c'mon - Michael Chiklis!
The Kids in the Hall: Complete Series Megaset - Oh yes, this is on my B-day wish list this year.
I would absolutely recommend Freaks and Geeks. Sadly, there's only one season of this show but it's worth a look. I'll warn you, most people aren't particularly drawn by the first or second episode, but keep watching and you'll love it. It stars Seth Rogen, Jason Seagel, James Franco, and several others that are big comedy stars now.
FRIENDS! Sex and the City! Those are the only two shows that I own. Don't get me wrong, I love Weeds and Enterogue (sp?) and a shit ton of other shows, but when I'm sitting down to watch a dvd of a show, I usually only watch one or two episodes at a time (unless I'm doing a marathon.. that's a completely different story.) I like Friends a lot because it doesn't really have an ongoing plot (other than the obvious Ross-Rachel, Monica-Chandler thing) so really, you can pick any episode to watch from any season and you won't have to remember what went on in the previous episodes to understand it. You know?