Just because your monitors don't display a 1920x1080 resolution doesn't mean you can't enjoy the benefits of HD. Standard definition through an NTSC tuner will be a real shock if you have never seen it on a computer monitor before. It is quite blurry and any imperfections in the signal will be quite apparant.
I watch TV on my Hitachi 19" CRT monitor all the time. But I try to avoid analog signals at all costs and stick with ATSC signals. Even though many shows are still only broadcast in SD, it is nice watching them in the digital format so you don't have to worry about wiggly lines and other artifacts caused by poor signals.
For the past 8 months, I have been using the Fusion5 Gold by DVICO and have been very happy with it. It has an NTSC tuner for analog signals and an LG ATSC tuner for digital channels. Only select shows on digital channels are actually broadcast in HD, but the SD shows look as clean as they ever will with ATSC (not particularly impressive, but tolerable). Shows broadcast in HD are of course absolutely stunning and a joy to watch. The shows are also broadcast in 5.1 surround sound which I take advantage of with my Cambridge Soundworks 2500 decoder box (6 years old, but still works fantastic).
The Fusion5 Gold can decode unencrypted QAM signals. For Comcast, this includes the local channels. It used to also include many cable HD channels, but in the past year, Comcast has really cracked down on keep their signals encrypted so you have to rent their box to view them.