Hoople - 6:01 pm on Aug 31, 2011 (gmt 0)
Where do you do the most reading about your niche? Is guest posting allowed there? Links allowed on meaninful an on topic comments? Ann Smarty's myblogguest DOT com site might be worth investigating too.
Some niche forums allow signature links after so many posts. They may be vauable than other forums (domain reputation).