Dealing with blog spam

I’m getting unundated with blog spam on this WordPress blog although Ido have an anti-spam plugin in place.  I am going to have to close posts for comments temporarily whilst I sort it out.

I’m sure this question has been asked many, many times before, but if anyone can recommend a really effective, free, anti-spam plugin for WordPress, please let me know .  Either email me at jane dot hart@c4lpt dot co dot uk or send me a tweet @C4LPT.