For a first AR, this is what I would get:
Lower: RRA, Bushie, Colt, LMT, or any name brand vendor, about $100
Upper: Same as above, preferably flat-top (A3) since it gives you the flexibility of mounting optics later on, but do get the detachable carry handle for now. About $95 for the upper, $95 for teh DCH
Barrel: Bushmaster 20" Gov't profile barrel assembly, pre-ban, with A2 FS. IMHO, this is a great barrel for the money, very close to what the military uses, fairly lightweight and pretty accurate. Runs about $220 from Bushmaster.
Bolt/Carrier/CH: Bushie, RRA, LMT Note: don't get a chrome plated carrier, but do get a carrier that is chrome lined in the bolt channel, about $120
Stock: A2 (fixed), M4 style (the RRA one is pretty good, and nice price) 6-position tele, or CAR style (4 position tele). ~$50 for the A2 assembly, ~$75 for the collapsables
LPK: buy a name brand from reputable vendor, runs about $60. Don't get any special triggers for now, the mil-spec LPKs are the most reliable and durable.
Total: $700-$750 (might be even lower if you shop around, but stick to name brand parts)
This should get you an assembled AR, one that is pretty basic, but works well and should be fairly easy to modify/accessorize later on.