One thing I like to do every day is pump out about 10 profile backlinks per day per site. I have about 20 sites so if I can't post all 20 links on 1 site it becomes quite the hassle (I'm also doing everything for as little cash as possible so finding efficient ways to do this by myself is my thing). Finding forums that have Visitor Messages is great because you get a dofollow link there and you can post as many as you want. Sometimes people will find them and report the spam but I like to think usually you just sort of go by unnoticed.

So here's what I do.

Google.com

search "Visitor Messages inurl:forum"

This usually brings up forums where they're discussing visitor messages so you know they must exist on the forum. Google just spat out who knows how many forum profiles where you can dump tons of links.

Register and view your public profile and you'll see the visitor message box and I'll dump about half, submit, dump the other half, submit. BOOM

These are mostly low PR but I do find a lot of high PR sites as well.

Sometimes you'll find forums where they've disabled them n such but that's to be expected.

You can get creative with this too if you know what you're looking for and can find a common keyword for forums that facilitate your specific need.