Link Building Tool #1: Link Diagnosis
Excellent tool to evaluate your incoming links and the incoming links of your competitors. By far, my favorite link building tool.

Link Building Tool #2: Xenu’s Link Sleuth
Not really a link building tool, but a great tool to find broken links on your site, 404 error pages and duplicate meta descriptions and page titles.

Link Building Tool #3: SEOMoz LinkFinder
Amazing free tool to find link building opportunities all over the web.

Link Building Tool #4: Majestic SEO
Another great competitive link intelligence tool that I use all the time.

Link Building Tool #5: SEOMoz Open Site Explorer
A much better alternative to Yahoo! Site Explorer.

Link Building Idea #1: Ask Business Partners
I’m sure you know a lot of people with websites and/or blogs. Ask these people to link to you! It doesn’t get any easier than this. These are some possible link sources: customers, vendors, co-workers, employees, business partners, relatives and friends.
Link Building Idea #2: Organize Events and Charities
People love supporting good causes and you can get a lot of links this way.
Link Building Idea #3: Give Awards
Organize contests and give the winners badges to put on their sites. These badges will naturally link to your site.
Link Building Idea #4: Get Links from Sites that Mention You
Sometimes websites mention you or your company but they don’t link to your site. Sometimes they even include your URL but it’s not clickable (not a link). Use the SEOMoz LinkFinder to find these sites and ask the webmasters to include a link to your website.
Link Building Idea #5: Ask Past Linkers to Link to You Again
Keep a list of people that link to your content and let them know when you have more similar content. If they linked to you in the past, they’re very likely to link to you again.