The following tip isn´t really all that new, and I told it quite often at search conferences before, but still there´re a lot of people, who are just desperatly looking for new sites to buy links on (yeah yeah, link buying is evil *blablabla*).
So besides the obvious stuff:
a) Looking at your competitor´s backlinks individually as well as looking at all your competitors, and try to come with sites, that link to two or more of them (like lists of sites in a specific niche, or review-sites etc.)
b) Typing in the keyword you wanna rank for into Google, and just scan the first 100 sites for websites, that aren´t selling links yet, and approach those with a nice offer.
You can also come up with great sites, using this technique:
1) Set up a Google AdWords Campaign (which you probably have already anyways)
2) Activate the Google Content Network, and don´t be to greedy on the CPC (yeah, we know the Content Network has a history of delivering crappy traffic, but when you use it right, and exclude shitty sites, you can indeed get good & cheap converting traffic)
3) Let the campaign on for a couple of days, and then run a Placement Performance Report.
NOW you´re getting all those sites, which Google showed your ad on (based on contextual targeting -> sites related to your keyword according to Big G. himself!). And it doesn´t stop there – you also see how many impressions & clicks you´ve been getting, which can give you a rough estimate how much traffic the site is actually getting (you can also check the site stats in Google Ad Planner, which will be pretty accurate, since it´s monetized via AdSense). And when you know how much traffic the site is getting, you can get a pretty good idea, of how much money the website owner will be making.
So you know 3 things:
1. The website owner wants to make money with his site (doah, he´s using AdSense)
2. You know how much traffic the site is getting, and have an idea how much money the website owner makes
3. Google thinks this site is relevant to your keyword / site
Now you can approach the website owner with a nice offer to buy “advertising space” on his site. I will even buy the whole advertising space of the AdSense block sometimes (which you can fill with a link-block yourself – with static links to your sites of course…), when the traffic isn´t all that great, and the guy doesn´t seem to make a lot of money. There´s just nothing better but clueless webmasters, who have great sites, but don´t make a lot of money with them