This is one of those good news/bad news deals. The good news: OnSale has the refurbished Westinghouse VK-42F240S-R 42-inch LCD TV for $499.99 (plus about $53 for shipping). That's one of the lowest prices I've seen on a 42-inch HDTV, particularly one that supports 1080p.
The bad news: Because it's a refurb, you get a 90-day warranty--and Westinghouse has a pretty poor reputation when it comes to customer service.
Now, that being said, I've owned a 46-inch Westinghouse LCD for years, and it's been a champ. The VK-42F240S-R (just rolls off the tongue, eh?) features 1,920x1,080 resolution, 2 HDMI inputs, 2 component inputs, and an ATSC/NTSC/ClearQAM tuner. It also has auto source detection, which I've always liked on my Westy.
I haven't found any reviews of this particular model, other than the single five-star user review on the product page. If you happen to own this LCD, share your thoughts about it in the comments.
Ultimately, the good news here is quite good--sweet price on a big TV--while the bad news isn't all that bad. You're not likely to find a better deal on a 42-inch 1080p TV.