A good Monitor is a LG 32h30. It has low input lag, a S-IPS panel, clear text (which is important for using as a monitor.) HSN just had the 37'' 37h30 model as deal of the day for 579. 96 dollars to deliver it on 6 easy pays. Best buy sells the 32'' for 599. Thats's where I bought mind.
I had a Vizio VLM26? but it over scan and the text was skinny and faded and the colors were horrible. Newegg has the LG 32F11. Nearly identical spec's for 379 but they unsurprisingly sold out. I wouldn't buy any TV to use as a monitor without testing how the text will look.
Shop around. I took my laptop into the store and out of all the models, the LG did text the best followed by Samsung. (They didn't have any sharps I could test.)
If you just want a monitor get the 24'' Dell U24 or the HP2475W. Although you can get a better dell on Dell's in the refurbished section. For the screen real estate and price, plus clear text, I'd go with a 32'' LG.
I wouldn't mess with a plasma. They have issues doing full screens of white. I have no idea why no one ever brings that up. If you open up Google and blow up its nice crisp white window it turns grayish. This makes text bleed and your eyeballs bleed. At least mine did when I owned my Samsung for a week.
Colors you can't beat but it does have issues if there is a lot of white on screen. You can even notice this in the stores if you are looking for it.