Supernatural is a top show, Rome is a great one too if you hadn't seen it before. Jericho is a little known one which I thught was excellent - couldn't believe it didn't stay on the air longer than it did. Watching a bit of Harper's Island on RTÉ 2 these days, seems decent enough. If you're into your Sci-fi and enjoyed the movie Serenity check out the original series Firefly....
And for just watching a once off show without worrying about series wide story arcs - hard to be any of the Law & Orders