Wikipedia links are all nofollow and won't help you that much, if at all.

I have found that back links from ezine is quite good...

Remember that only Google pays attention to the nofollow tag so Wiki links are still valuable in terms of SEO for Yahoo and Bing. Also from experience you can get a handful of visitors each day from a Wiki link.

Google has stated that they don't pay much attention to the nofollow attribute any more. I think it was Matt Cuts that I heard say that but can't remember for sure.

Wiki can be used nicely as a doorway page to block your competitors. As 9/10 depending on your niche will rank in the top 3 and outrank any competitors you have.

And you act sneakily and use Wiki properly. You can make it a doorway page for people to come to your site rather than a competitor's as you have the rank blocker.

I have a link there in the one area in which I am a super expert and it goes to a site that is primarily content written for people who are trying to deal with a specific problem in a super specific niche. I mostly did it so that people who were searching on the keyword term would find a resource.

For me it was just one more way for people to find out about me. I don't care what Google decides to do - if someone is searching on that term, they'll find me. In the end, that's really all that matters. However, I wouldn't do it for my more commercial sites because it's too likely to be seen as spam and deleted.

Bottom line - it all depends on what your site is about and if it's a resource or something else.