If you want to use them in your Web site, in your product, on your living room wall, on your next album cover, or whatever comes to mind, you have my permission.
You don't even need to ask, though I enjoy getting email as much as anyone. However, if you sell something that contains my pictures, I would like a free copy. Don't try to sell me a discount copy or advertising space - this is my hobby, and I pay enough for it already! ;-)
If you use a picture on your Web site, I'd appreciate a link back to my home page. However, please understand that I prefer to be a "leaf" on the web - that is, I'm not here to provide links or ad space, just pictures and stuff.