Based on the research I've done, any of the high-end screens from Samsung or NEC-Mitsubishi are hard to beat in the 17-19" category. Large contrast ratios, fast response times and most have nice looking chassis as well. Not to mention they have better warranties than what Apple and others offer. I think NEC is 3 years right out of the box for example.
As for where to buy, I would pick a couple models you like
Samsung
NEC-Mitsubishi
...and then compare availability and prices at Buy.com, Outpost.com and CDW (if you don't live in Illinois). Macmall also carries 3rd party monitors I think.