I'm buying an AR15 lower
half (DPMS or Bushmaster), but don't know which
vendor in Shotgun News to trust.
This'll be my first AR. Just want it to be
accurate. I'm a shooter not a collector.
Thought I'd buy a lower half now and buy an
upper half later (due to current budget).

Here's some dealers in Shotgun News I found:
KY Imports
Hoplite
Jeff's Shooters Supply
Kiesler's Wholesale

They have lower halves in the $250-$275 range.

Any recommendation?

Go Factory Direct.  Try Rock River Arms.  I have heard allot of good things about them.   I think they are all pretty equal.  But thats just me.

do yourself a favor and buy a lower from Pete in NH. best prices around. to boot, you'll get a high-cap mag. www.ar15.com/forums/topic.html?id=83298

Have to second the reccomendation for "Pete in NH"  go with the RRA lower.  I just got one from  him and it is perfect and he's a good guy to do business with.  I put a bushmaster upper on it and it fits and fuctions perfectly.  
  Good luck!