Just a suggestion or two...
1- Create a sponsor link that would list all who have donated for that month. Create a tiered system in which Gold members donate at least X amount, Silver donate at least Y amount and Bronze donate Z amount. Everyone likes to see their name or handle in a favorable light. The alternative would be to list their status under their username, along with or instead of players names.
2- If a dedicated server is involved, could you offer other simple services? Something along the lines of, donate so much per year and get a mail box that has a "firstname.lastname@example.org" address. That would be pretty cool.
In any case, put me down on the list for sponsoring a month's worth of service. Heck, I might be persuaded to take care of two months.