Prison Break is good, IMO. Not old, and not overlooked, so you probably have already watched Season 1.
Also, I noticed you have two Sorkin shows in your list; Sports Night and Studio 60. The West Wing is a great 7 season series that would kill your bus rides from now until August. Season 1-4 are great.
I'd add Dexter to the list of good shows that nobody knows about.
It is a dark (most of the time) drama which has the main character as a serial killer. I was very skeptical, but thought I would give one episode a try, then another, then another. By Episode 4 or 5 I was totally hooked and had to pull down the whole series. It originally aired on Showtime.
http://www.tvrage.com/Dexter
I second the votes for The Shield and The Wire.
Given that I liked Dexter, The Shield, and The Wire, does anyone know of any other shows that I might try next? The Sopranos and Brotherhood are already on the list, but I just havent had time to watch them.