Get spammer's limbo for phpBB. Of course the BEST thing you could do about the spammer problem is to switch to vBulletin. There are many more plug-ins available for vBulletin to deal with spam.

You can put a serious dent in spam by blocking the following:
all e-mails ending with.info,.RU,.WS
block all IPs coming out of Russia (and all former Soviet republics), China, and India. Those three are responsible for 90% of forum spam. Russia is the clear leader, but the other two make up the remainder.