Here's the (not-so) short version:
If you're going to view from 20 ft away, you need to go big. kinda doubt you're really 20 ft away (that's a LOT), but even if you're 14ft away or more, you gotta go with either a 46" or 52" tv if you want to make out any sort of level of detail.
Circuit City going out of buisness sales are unlikely to be any help for you. They get bought out by a liquidation company, which marks everything up, and then slowly brings it down with % off. If it JUST started the sell-off, you can get better deals elsewhere. If it's been going on a while, the price might be ok, but the decent stuff is long gone. Better off with the Black Friday (day after Thanksgiving) sales, or anytime betwen now and Christmas is supposed to be good this year due to over-supply in the TV market with the down economy.
LCD would be my recommendation. Can plug the computer in directly with a VGA (monitor) cable connection, will look exactly like a regular computer monitor. They'll all have USB connections, but mostly just to put a thumb drive in for a picture show or whatnot. I've never used mine, aside from a firmware update. Get the 1080p tv. You can save money by getting 720p if it's an issue, but why get one that's already out of date, and with blu-ray as an option, and even cable tv at 1080i, no reason to limit yourself, considering how cheap the tvs are getting.
With a small child, why NOT put it on the wall? Would prevent them from touching it, smearing the screen, hitting it with things, knocking it onto themselves, etc. I'd definitely recommend that, if you have a space that can support it. Better visability from a distance, as well.
If you're deadset on NOT putting it on the wall, and you have decent floorspace, I don't think the LCD vs Plasma debate is something you should be talking about. Given your distance from the TV and your desire for it to not be on the wall, a DLP (thin projection) tv is probably the answer for you. You can get these cheaper than the thin tvs, and in larger sizes. For the price of my 46" LCD, a friend of mine got a 60" Sony DLP, and it looks great. It worked in his living room whereas I had to hang mine on the wall, so I couldn't do the same tv, so it's definitely a matter of the room setup. But given what you've said, could be the answer. Same HD screen resolution, not as thick as old projections, better viewing angle. And much cheaper if you want a big screen, compared to LCD/Plasma tv sets.
For example (and this is the first site I looked at, didn't comparison shop or check more prices), BestBuy has a 56" Samsung Slim-Depth DLP TV HL56A650 (1080p) for $1200. It's on sale, but even regular price is $1499, so with a little deal shopping, can find a good deal on that. Depends on how you feel about brands (Samsung is a pretty good one), what you want to spend, size you need, etc. That tv would probably be where I'd start...