Most unsolicited commercial email tries to get its readers to buy something, but recently I had some spam that was the other way around - they wanted to give me money! Specifically, they wanted to buy ad space on one of my sites. Now, given that I don't have any costs involved in running the site in question (the hosting and domain name were donated), I don't feel I have the right to put ads on the site. I wouldn't want to anyway - it's a better site for not having ads, and it's not like the amount of money involved is likely to make the slightest bit of difference to the quality of my life. For the same reasons I don't have ads on this site (maybe if I could make enough money from the ads to give up my day job it would be a different story but none of my websites has anywhere near that amount of traffic!)
Even so, it took me a moment to decide whether to reply with a polite "no thank you" or to press the "report as spam" button. In the end I decided on the latter course of action - it's still unsolicited commercial email even if it's buying instead of selling. And one of the last things the internet needs is more advertising. It's kind of interesting though that advertisers (or ad brokers at least) are starting to court webmasters - it always seemed to me that the supply of advertising space on the internet vastly outstripped the demand, but maybe that's changing.
Similarly, my web host recently sent me a coupon for $100 of free Google ads - I have no use for them myself (I don't think anyone interested in what I have to say here is going to find it via an ad) but I hope I'll be able to donate them to someone who does have a use for them.