Here are 3 solutions for fighting spam:
Get the plugin: http://www.ioerror.us/software/bad-behavior/
Does NOT work at godaddy
Spam Karma 2
Get the plugin: http://unknowngenius.com/blog/wordpress/spam-karma/
Do NOT ask 'Which is best because....' or 'Which one do you suggest I get' or any variation of that - they are ALL good and yes, they can all be used together.
SK2 will run all existing comments through it's filters to catch spam already there.
CJD Spam Nuke from http://chrisjdavis.org/category/wp-hacks will also ID and let you remove spam with one click
Captcha (where you have to type words in to verify you are a human) are NOT effective. You will still get spammed. So use one of the above.
You may also see little 'Donate' buttons on the above sites. As their work was given freely and saves you masses of time (do you want to delete spam by hand every morning?), saying Thanks by dropping a tip into their jar would be appreciated I'm sure.