http://www.del-ton.com/AR_15_Rifle_Kits_20_s/58.htm
http://www.del-ton.com/AR_15_Rifle_Kits_16_s/57.htm
Kits for carbine and 20" full sized M16. You can customize them and they ship to you disassembled and you can pick foregrip, upper, barrel, lower receiver, feedramps, etc., etc., and it is more affordable than buying strictly brand name i.e. DPMS or Bushmaster or Rock River Arms (Rock River Arms, BTW, I have heard glowing reviews about on affordability and performance)
Click on the link and rifle you want to make then it lets you accessorize
Edit: You will probably have to get a lower if you get one of the above. Says it's not included anyway.
EditII: Here's what I have picked out.
# 16 LW Rifle Kit -Barrel: DTI 16" 1x9 Light Weight Barrel
# 16 Rifle Kit -Handguards:YHM 4 Rail Light Weight Free Float Tube
# Rifle Kit -BC:Standard Bolt & Carrier
# Rifle Kit -Buttstock:M4 Buttstock - Black
# Rifle Kit -Carrying Handle: Detachable Carrying Handle (Flat Top's ONLY)
# Rifle Kit -Flash Hiders:3 Prong Flash Hider
# Rifle Kit -Gas Blocks:YHM Specter Gas Block
# Rifle Kit -Grips:Ergo Grip - Ambi
# Rifle Kit -Lower Parts:Standard Lower Parts
# Rifle Kit -T Handle:Standard Charging Handle
# Rifle Kit -Uppers:Flat Top Upper with M4 Feed Ramps
Also picked were EoTech 512 Holo sight and Harris LM Non swivel bipod. Total with UPS 3 day: $1,189.48