I'd probably just give it to them, depending. If it was a high budget nonprofit that I wasn't involved with, that wanted an 8x10 cover photo for its worldwide brochure, I might charge them $100, or maybe more if it was something really unique; but otherwise probably not.
If you're a commercial photographer or trying to be one, it's more of a dilemma as you can't just give your stuff away in one case and charge in another, but if you do it for your own enjoyment, and selling any photo is just an incidental issue, then do what makes you feel 'good' about it.
You should definitely ask to be credited for the photo, and can ask for a link to your website if you want. Be sure to specify, regardless of who it is, exactly where and what they can use it for. That way you're not giving the rights to the photo away, just allowing them to use it in the way you've allowed. If they want to use it later for something else, they can ask again.
Most everyone has a hard time with this issue; if it's for nonprofit use, I don't charge, but then I don't see anything wrong with charging a bit just so you feel it's fair; if it's connected to anything for their profit, or they want you to do some post processing on the file or send them prints, then charge for it...but then you have to decide how much 8^)
Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo