In reply to Heike:
I use Fotoquote software and it's quoting £150.00 for a 1/2 page spread in a UK consumer magazine, circulation under 10,000. I'd imagine that's top dollar, so to speak, so I'd negotiate down depending on which magazine it is.
Saying that, it's a moot point if you give people the image first in good faith. I'm due payment from a certain MB magazine, who used my image in their last issue but are proving elusive in responding to my emails.