Sorry Jo, I completely disagree that 'the links should come naturally'. If you have a boring, functional product that doesn't lend itself to social media, or even if your content is just something that users won't naturally link to, you're stuck.
Elissa - one of the best ways I've found is to put in time to researching the bloggers in your space, crafting unique pitch emails for each one, writing some great content for them and providing a decent guest post, or asking them to include a link in one of their posts that relates to your page.
Blogger Linkup/My Blog Guest etc won't generally serve up decent quality sites any more you need to do this research manually, but you should be able to get some good links out of it!