I use the wp-polls plugin from wordpress. I like to use it because not only can I put the polls in the forum, but can also include them into posts or pages in the associated blog or multisite blogs.

We actually created a whole sub-set forum just for polls, you can see it at.. http://podaid.com/forum/

the main problem with wp polls for a lot of our users is that general users cannot create polls…  but anyone can put an already created poll in a post via shortcode…

good news is that I have started working on a polls plugin for Simple Press….  I already have a working prototype up and running…  shooting to release the plugin this summer…