For the benefit of the next person: don't ever sell donations. Sell sponsorships/bragging rights/etc. In addition to converting better this reduces payment processor risk. I would strongly suggest doing this in preference to pre-orders, too, since pre-orders are very risky. Structurally guaranteeing that 100% of your customers have not received shipment is a bad place to be in life! You are not Valve.
Bronze Sponsor: You get a 16x16 icon next to your username on our website delivered immediately plus, as a bonus, a free copy of the game when it comes out. $10
Silver Sponsor: As above, icon is silver. $20
Gold Sponsor: As above, icon is gold, you get listed in credits. $40
This is a very solid idea. As an alternative, you can use a payment processor that deals with PayPal and credit card companies on your behalf. With something like FastSpring.com, you get paid as long as the transactions are genuine (e.g., excluding credit card fraud). You never have to deal with PayPal, Google Checkout, or frozen account bullshit.
Bronze Sponsor: You get a 16x16 icon next to your username on our website delivered immediately plus, as a bonus, a free copy of the game when it comes out. $10
Silver Sponsor: As above, icon is silver. $20
Gold Sponsor: As above, icon is gold, you get listed in credits. $40