The best thing you can do when you see spam is to avoid replying to the topic or clicking their links (and thus give it unworthy attention) and just click Report to moderator. One time per spambot user is enough (so if you see multiple spam posts by one user, you only need to do it for one of its messages).
Besides from that, yes, some tighter registration controls could be nice, but as far as I know it's hard to implement on the forum.