Pepid is probably outside your budget. It is not a bad product, but it is expensive and it is an annual subscription which does expire, ending your access to the reference. Check out -Skyscape: EMS/Paramedic
They carry the first title Daphne posted, and several other references. There are two advantages to Skyscape over other products. They use a small reader which installs to the device, and the titles are installed to an SD card, which saves you device memory. The titles also remain active after they expire, you are just no longer entitled to updates when they become available. I've personally used the ALS reference for a few years now (going back to my dreaded PALM days) and I still go through it every now and then.