No better tool than SEOMoz's
Open Site Explorer. Check out your competition's backlink strategies. Look at the directories your competition is listed in from the root page tab - and make sure you get listed in those directories too.
Small example - I noticed one of my competitors was getting a ton of linkage from wordpress.org, which is a highly credible site. I did a search on wordpress for the company and it turns out that the owner of the company had created a wordpress theme (not a very popular one), but by having his profile in the wordpress site with a link to his company, Google indexes his company higher in the natural rankings because wordpress is a highly authoritative site and trusted, so that company goes higher. It's not so much about quantity of links as it is a combination of quantity and quality links. If you pay for submission and sudddenly your traffic goes way up, Google is going to red flag it and may penalize you. Any link strategy should be carefully built and over time. The pops get you in trouble from what I've heard, so try to avoid those.
It's interesting, and I know everyone isn't going to create a wordpress theme to get higher in the rankings, but stuff like that and thinking outside of the box and hard work (2 hours a day min) will improve your rankings (Er, uh, so I'm told - slowly but surely for me, anyway)...