I wouldn't build all of your backlinks in one go, too many at one given time may harm your rankings. But otherwise, a steady flow using the following techniques could be useful:
Directory submission to quality directorys
Article writing & submission
Press Releases
Social Networking to dofollow networks
Dofollow blog comments
Related forum signatures
Linkbaiting
Link exchange with similar themed sites (on topic, but not direct competition).
Blog reviews in good ranking blogs.
Some of the above methods are free and paid, it depends on your budget. One site I have has today gone within the top two for one of my main keywords using these techniques, it took about 3-4 months for the site to settle though and is still not a stable rank. I'm still waiting for Google to settle it.
A breakdown of what I paid is $25 for both 1500 directory submission (about 75% acceptance), & 500 articles (60% acceptance) - I bought the package, but had to submit & confirm them myself, took me about 4-5 hours.
$8 for 100 social bookmarks submitted by somebody I know.
A further 200+ articles written and submitted by myself using an article spinner. Find dofollow blogs using the firefox
seo plugin that highlights nofollow links in red. Pretty easy to find using Google, but sometimes its like finding a needle in a haystack as most blogs thesedays are nofollow. The ones you find could be priceless.
Linkbaiting I have not tried yet and still reading into it, I have heard good things about it, but also some bad things, like the money.co.uk stunt and how it backfired. Article submission is a form of link-baiting, whereas webmasters are allowed to used your article for their content with your linkback to your site, as is template creation for the less imaginitive. Create a template for your favourite app, maybe WP or Joomla and add your link to the bottom, then allow other to use it. I have never used this technique, only come across it in reading.
Blog writing I think can be quite useful, but it requires payment to the top blogs. They will review the product like on your site on their blog with a link back to your site. It can be useful if the blog reviewing your site is strongly thought of in Google and the content of their review is good. Better 10 strong links than 100 weak links in my opinion.
Forums I dont have the time to post much, like this one. Digital Point, I have been a member since 2005 and only posted about 80 posts

But a lot of people swear by them.
I usually look at around 1000 backlinks to my niche site to get me a stable ranking in the top 2/3 pages for my main keywords. I'm still trying to crack loans in the
SEO department, my own little challenge, but it is going to take a hell of a lot more than 1000 backlinks using these techniques I think.
You could also post on some classifieds like craigslist, etc may help. Other than that, good content and natural backlinking
It helps to spend a little, but not a lot. It costs a lot more in time.
Terry