What DLP projection TV's can display 1080p (1920x1080) from a PC and
via what interface?  Preferably >50" and <$2000 USD.

The hp md5880n can do it via hdmi.  Any 1080p tv should be able to do
it via hdmi.  You simply need a video card with a dvi out and
dvi->hdmi converter (simple and cheap device as hdmi is backward
compatible with dvi).  There are not that many true 1080p tvs.  They
are just starting to come out.  The hp one was pretty much the only
from last year's models that was 1080p through its inputs.

The new sony's can do it as well via hdmi, but they are not dlp, they are lcos.

I have recently shopped for a big screen HD DLP with 1080p. You will
most likely not be able to find one that is >50" and <$2,000.  A 50"+
1080p DLP will start around $2800 in the US.  My shopping was done at
the major online stores, Best Buy, Circuit City, Sears, and some
specialty stores. If you wait another 6 months - 1 year, they will
come down in price.