Usually a 32-incher is the best you can hope to find at this price point. But the highly rated Proscan 40LD45Q offers 40 inches of high-def viewing goodness.
If I can wax nostalgic for a moment, I can remember when finding a 32-inch LCD for $399 was a big, big deal. (Even today I see them selling for that much and more.)
Now Walmart has the 40-inch Proscan 40LD45Q LCD HDTV for $399 shipped (plus sales tax in most states). That's pretty fantastic.
The Proscan is a full 1080p TV with three HDMI inputs, a VGA input (in case you want to pair it with a PC), and a 2,000:1 contrast ratio. It also sports an ATSC tuner in case you prefer free, over-the-air HD broadcasts to pricey cable or satellite.
Obviously Proscan isn't a household name like Sony or Toshiba--in fact, it's the kind you typically see only at a place like Wal-Mart.
However, I think the customer reviews speak volumes. This model currently has 273 of them, with an average of 4.5 stars out of 5. The only complaint you tend to see is with audio quality, but in my experience, all HDTVs have crummy built-in speakers. That's why most folks add a home-theater speaker system or the like.
If memory serves, this is the lowest price I've seen on a 40-inch HDTV. It could be a perfect choice for the den, bedroom, or even living room.
Bonus deal: I rarely see compelling prices on Flip Video camcorders, but here's one: Buy.com has the refurbished 720p Flip Video MinoHD for $89.99 shipped. This one has 4GB of storage, enough for an hour of HD video.