Use PayPal only if you like having your funds frozen. They also don't allow currency conversion and are prone to "friendly fraud" (see: chargeback).
Best are: Liberty Reserve, c-gold, Pecunix, Loom, e-dinar, MoneyBookers (with written permission to do currency exchange), and possibly AlertPay (again with written permission to do currency exchange).
Some other methods: money order, bank transfer, cash (in person or via postal mail), physical gold and silver, gold and silver certificates, hawala, ripplepay (prone to fragmentation problems), and LETS/Time Dollars.
Want more suggestions? I can go on and on.