Unless you're planning on connecting your XBox, etc to your monitor as well, I would personally stick with the PC LCD. At this point, resolutions, quality, et al are virtually the same in all of them so it is really a matter of extra features.
As well, I wouldn't recommend anything larger than 30" for a PC monitor, since you're not sitting more than a couple of feet away from the screen generally, and it'll get tedious to be constantly looking from end to end on a 42" screen (I'm also not sure how great a plasma would be as a general-use monitor).
Looking at the specs of the 26" monitor and TV. You might want to note that the LCD TV doesn't have DVI inputs, and at that size, you want to be connected via DVI, not VGA, for quality's sake. Not sure if it matters, but the LCD TV is also about 4 lbs heavier with the stand, and 9 lbs heavier without.
If you were planning on using this both as your television and PC monitor, I'd say go for the TV (though you can just as easily use your PC with a TV tuner card and then have recording capabilities as well...). Since you said it's mostly for general use, with periodic movies, you'd be more than fine with the PC LCD. Quality for movies is almost exactly the same (if not exactly the same) and for general browsing, it'll be a better experience. This, of course, is on top of the deal-breaking lack of DVI input on the TV.