Backlinks How and where to get them?

Hey gang. I am working on a hand full of websites. I need back links and want to know how everyone is getting them?
I use social media bookmarking sites through onlywire to social book mark back to my sites. I do not have the budget to buy links.
How do I get quality links? Link trading? If that is the case how do you guys link trade? Tools?

Any help would be much appreciated!
-J

the search function still worked the last time I checked

Look for lists of social media, social bookmarking, web 2.0 sites to create an account and post a link

To find these lists, you should follow cool.dude's suggestion