At level 70 you can obtain a reputation pvp set through each of the reputation places.

• Thrallmar / Honor Hold
• Caverns of Time
• Lower City
• Shat`tra(sp)
• Cenarian Expedition

After you buy this set of armor you are pretty much up to par with most anyone in battlegrounds. (no you can't 1v1 a s3-s4 geared player)
This armor set is actually quite good to get you started into pvp.