What is the best tv to buy?

This is a topic best suited for our Home Audio and Video forum, but I'll do a quick rundown of the answers you seek:
1.) Flat panel simply refers to the form factor...flat/skinny. You then likely specify either Plasma or LCD, which are types of displays. In short, plasmas suffer from burn-in (if a logo or news tickers is on long enough it will become permanently 'burned' on the screen, even after you change channels) while LCDs are still not quite as advanced as plasmas when concerned with display quality in large (44"+) models.

2.) Brand/specifications I'll leave up to the videophiles to go over since it's a delicate balance of price and quality.

3.) HDMI is the optimal digital connection for TVs, offering better quality than composite, component, and S-Video connections. It's much like saying you'd rather have a DVI connection from your computer to monitor than a VGA one.

4.) HD Ready is the terminology used to specify the TV is capable of displaying HD-quality programming but does not include an HDTV tuner. The omission of that reduces the cost of the TV, but means you have to purchase one later if the cable/satellite box from your provider does not include an HDTV tuner.

Hope this helps,
John