I dont think just getting any old niche link make it strong - yes its make its stonger than a vanilla backlink. I always stick with the obvious and say article marketing and Press releases make for very srong backlinks
That's also best for a website too, but it's quite better in my experience to get 10 irrelevant links from at least PR 1 website then having 1 relevant link from PR0 - PR1 site. It has proven to work nice for me. I'd definitely would love to try blog commenting to see how it works, but article marketing keeps being #1 for links for independent traffic and traffic you can do solely on your own without JV's.
I would also suggest inclusion in Yahoo directory and DMOZ...if you are in there then those are two pretty strong backlinks.
Here are the 3 ways to get backlinks: 1. Submit Articles to Directories This is the most popular way of making backlinks for your site. Many fortune 500 companies get there sites ranked very quickly by using this technique. It is a sure fire way to know that you have a good link from a high page rank site. I recommend in submitting your articles to as many high page rank sites as you possibly can. You should also make sure that you are submitting articles every single day until your site reaches the number one page in the search engines. 2. Press Release You can really get a high PR boost if you submit some press releases. A press release for your landing page can be about your site just starting up, what it has to offer and what good it can do for people. You can also write a press release whenever there are changes made to your site as well. There are many press release directory sites that have high PR so you should definitely submit them to those sites. 3. Forum Posting Forum posting can also be a very good thing. I know it can be kind of annoying with keeping track of where you posted and such, but it is really a good way to get your site indexed quickly. All you have to do is make sure that you put your site in the signature line and post a few things to people that have questions. Maybe you can even ask a question or two for yourself.
Use ibp or similar software to find pages to exchange links. You can use a mail template to contact with a lots pages.
Do daily blog comments, forum postings, social bookmarkings, and article submissions to start building up.
Blog posts on different IP's; videos; articles and a couple of automated linking tools are my favorites. I really like the new WP Plugin for backlinks - very cool (see my sig)
One word, article marketing and guest blogging on sites that are relevant to yours (ok, that was more then one word ;-)) SY