Stargate SG1 (seasons 1-8) has to be my all time fav. It's the most realistic and down to earth sci-fi show around because it's set in our time.
After that...well
Without a Trace
The West Wing
Will & Grace (Jack buys an apron, Grace looks at it "...oh...kiss the cook." "WHAT!!!! Kiss the cook!!!!...that's an O???")
As a rule I don't watch TV unless I'm visiting mom or travelling. If I see a show that looks good I'll wait for it to come out on DVD and then rent it. If I really like it then I'll buy then as I have done (or am doing) with all the above mentioned shows.
Other shows I like but are not on my favourites list are
The Star Treks (except Enterprise cause I haven't seen it),
Six Feet Under,
Stargate Atlantis
Battlestar Galactica (old and new)
Babylon 5
Boston Legal (I haven't seen enough episodes yet but the presence of both William Shatner and Candice Bergen make this a prime candidate)
Smallville
MacGyver (DVD box sets of the first few seasons are 20$ at Wal-Mart right now...that's a good deal)
Absolutely Fabulous
Are you being served?
Coronation Street
Dr Who (I know there are several of these shows around...it's the one that was airing on the Sci-Fi network in the States this spring. I saw a few episodes and liked it)
Monk
There are others but I can't think of them right now. :-)