If you're served your meal by a good waiter or waitress, you give them a tip. If you're walking down the street and you see a musician performing with his guitar case open, you may throw a dollar inside of it.
Why not apply this kind of thinking to websites you like? If you like what I'm doing here, give me a tip. If you're a frequent visitor to this site but don't have time to comment on anything, why don't you give me a tip to show your approval?
I'd prefer that you tip using Paypal (since they don't take a percentage of it for themselves), but feel free to use the Amazon Honor System if you're more comfortable with it.