Google it out : "Travel powered by vbulletin" Replace "Travel" with your topic or niche. you'll get lot of forums in result. Good luck.
If you're trying to get traffic to your travel websites posting in travel forums vs non related forums with higher PR I know posting in the travel forums would be better. If you are posting good content people will visit your sites since you're hitting your target market. Forget about forum PR. By the time all the PR is spread out to all the posts it adds up to nothing. Your travel forum posts will help you more wiht search and real traffic.
I was also looking for the high pr dofollow forums list but I searched in the google and found and I bookmarked the page. You can find useful dofollow forums here : http://expertseoservice.wordpress.com/2008/09/25/forum-post-best-way-to-increase-traffic/
Thanks for the great list forum directory. But whats the best way to use it? To register with the boards I am interested in and start writing there or contacting the webmasters for linkexchange or paid links? How are you gonna use this?
dbinto has it right - post meaningful responses and comments and people will eventually follow through to your blog or website. Don't over post and don't spam. Contribute and you will be fine.