Well according to Google "Currently, AdSense publishers may place up to three AdSense for content units on one webpage. This includes a maximum of one 300x600 ad unit per page. You may also place a maximum of three link units and two search boxes on each webpage. You may place up to three link units on a page, in addition to the three standard ad units, and two search boxes. " Reference: http://support.google.com/adsense/bin/answer.py?hl=en&answer=1346295#Google_ad_limit_per_page
http://wordpress.org/extend/plugins/tags/adsense there are a bunch of plugins for adnsense on this page. Try a few and see if you like.