How to build backlink

I've been thinking the effective way to increase backlink and eventually PR. Several general options are:
*Submit to directory. Not very effective because you need to set reciprocal link. The quality of links depends on the directory PR and the page PR where your web is listed. The best directory you can be listed is Yahoo directory and dmoz. But it is hard to be listed in and expensive for Yahoo directory.
*Link exchange. Just like 'submit to directory', you need to set reciprocal link. Your link should be in page which have PR.
*Blog commenting. Not very effective, because your comment usually in non PR post. Usually old post will be hard to be found by Google if the blog does not have proper structure. Trying to be a top commentator is also not a good option, because you have to do it every month. Blogger usually reset the numbers at the start of the month. Other option is to give comments on the 'popular post' on the blog, because the home of the blog usually gives link to the 'popular post'. But this is also not very effective if many people comment on that post, the PR pass will be low.
*Forum. Same like commenting.
*Article submission. Does your article have PR on the article directory? How many clicks does it takes to visit your page from the homepage. The more clicks you need to do, means your article is not in the right place. I have checked ezinearticles, it has PR of 6. To find my article I need to first click the 'expert author' link (PR 6). If you have lots of articles there, you can click the 'next 100' link, but too bad it does not have PR on that page. If I click the First initial of my name, there is no PR too on that page. Well I think ezinearticles does not gives good PR to our web. I think their URL is not SEO friendly. Next I try ehow.com (PR 7, better than ezinearticles). They have better URL structure. If you have article there, you might have PR for the article. Internet marketing was promoting ezinearticles and everybody writes there including me. When I write this article, I just realize that it was a mistake. I think I should move all articles to ehow.com or website that is similar that that. BTW, I also make my own article directory Get Various Tips from finance to health - Welcome to TopEasyTips.com, which I made with proper structure. I have also created programming articles and submit it to a website that accept my articles. I have three articles. All have PR3 and it is linking to my blog.
*Making wordpress themes. I haven't try this before. But if you have great theme and lots of people using it then you can have lots of backlink from the theme footer. Yes people can delete it, but lots of people don't.
*Making wordpress plugin. Two months ago I make a plugin and it has PR 1 at wordpress.org. I have link to my blog from there. If people use my plugin at their blog, they will give me backlink too, because I put a small 'powered by myblog' link at the plugin.
*Making a super post that people will link from their blog. You need to work hard on this and make sure lots of people read it.

So for me the best way to get back link in order are:
-Create useful plugin
-Create theme
-Create articles and submit it the article directory.

Some tips:
-You can hire people to write plugin or theme for you.
-Submit your articles to new article directory just like my topeasytips.com. You got nothing to lose. When they become big, your article usually will be easily found. Remember the number of clicks you need to reach your article? If they have lots of article, they will have paging system on their website. If you submit early, you won't be in the last page.