I have a GX Pump's CS4 and a L3 (battery powered). The CS$ is awesome and will fill tanks. The L3 (same as a CS3) fills airguns great. The L3 is great for when you're in the field and don't have an external power source. They use Makita Batteries, so spares are easy to find. You can check out the specs of all the GX Pump Compressors here.
GX CS4 Portable PCP Air Compressor, 350W Powerful Motor,Max 5800Psi/40Mpa, Water and Fans Cooling, 5 Hours Continous Work, 12V Auto Stop,for PCP Air Rifle Paintball
gxpumpofficial.com
Purchasing direct from GX Pumps will save you sales tax and they also have a coupon code (GX10OFF) that will get you a 10% discount on any compressor purchase.
I have had my CS4 for going on 3 years and it's still working great. They make a good compressor and have a great reputation and great customer support.