Sell access to commands, like the ability to use fun things like /hat, and /nick, some harmless commands. Give them bolded or highlighted names in chat, or the ability to use color codes like &2 and &k.
Depending on the type of server, you can also include premium access to certain areas of your server. If you have a minigame server, you can have premium members be allowed to use beta tested games, as well as some exclusive gametypes. On a factions server, you can sell items or faction power, or even large plots. On a survival server, you can sell statues in the main spawn area, where anyone who has given enough can have their skin built by the staff.
Be careful though, ive seen many servers starve for donations becuase of their high expectations. Start your prices at modest, low intervals. Not alot of people donate to a server that starts out their cheapest package at $20. Small intervals make a donator feel more comfortable in their purchase if they have options like $2, $3, $5, $10.
And yes i am going to check out your server
