An interesting thread over at reddit suggests there just might not be a lot of great TV around for the watching. Most comments are around the same few shows. I've excerpted one summary comment below.
In the thread, the top suggestion was Deadwood, while the most praised show not mentioned below was Rome. Everyone said Rome was fantastic, but that it was canceled after two seasons because it had cost too much to make. Honorable mentions to Weeds and Californication, but presumably they aren't everyone's cup of tea.
The best of all time in order of greatness:
-The Wire (many many times better than anything else)
-Sopranos
-Mad Men
-West Wing
-Breaking Bad
-Big Love (good until this past season)
-Six Feet Under
-Eastbound and Down--funny but does not deserve to be mentioned with the above shows (only 1 season so far)-Also extremely good but only done as a mini-series:
-Band of Brothers
-Generation Kill (done by many of the same folks that did The Wire)
-The Corner (done by many of the same folks that did The Wire)Some older series you might consider:
-Mash--that'll keep you busy for a while and it never gets old
-X-FilesHaven't seen these myself but I hear they're very good:
-Deadwood
-Dexter
-Oz (you may need to prepare yourself mentally for this one...kind of rough)
-The Shield