I accept PayPal eCheck (US only; preferred form of payment), PayPal, credit cards, and personal checks (US only).
For projects $500 and over, a deposit of $250 will reserve your slot. 50% of your balance is due before the project begins. The final balance is due upon completion and before your manuscript is sent to you. For projects less than $500, the deposit is 50% of your total.
I issue invoices through FreshBooks, which lets you pay through PayPal or by credit card.