Amazon is a great place to grab a TV since they have the best customer service, price matching, return policies ever. But you have to wait for a good deal to pop up. You can use
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www.slickdeals.net or similar. Amazon doesn't charge tax or shipping (usually) and they often ship from Fernley so you get your order fast.
99% of the time, 99% of people aren't utilizing 1080P vs 720P. Unless you'll be using it as a computer monitor on a regular basis (not a good idea with plasmas due to potential burn-in) or sitting way too close while watching Blu-Ray, a decent 720P plasma will give almost everyone a MUCH better ROI.
Check this out:
http://satellitetvguru.net/720p-vs-1080p/
I went to BB before my Samsung 50" 1080P plasma arrived from Dell. They had my TV right next to the 720P version and with 1080P content from like 8 feet away, you could only tell the difference with large font. The large font had barely noticeable jagged edges on the 720P set.
Honestly I'd rate a TV solely by trustworthy reviews of the exact model (articles on C-Net, Consumer Reports, AVS Forum, etc.) armed with the knowledge to determine what's important for your particular usage. The specs listed are often completely misleading so competent reviews become quite important.
And the newest features (120/240hz, LED backlighting, internet capable) are almost never worth the cost they add. A name brand solid 60hz 1080P 42" LCD should be between $425 and $500. A name brand solid 720P Plasma should be a touch less, or at least easier to find a deal on.