hookshot
As hyperion suggests, "niche research" means exactly what it implies. I think that this is probably the most brought up and least discussed topic in affiliate marketing, and the reason is pretty clear: the methodology behind how a successful marketer chooses, tests and ultimately dives into a niche is pretty serious stuff -- "my secret AdWords strategy that puts my ads on page one every time!" kind of stuff is just fluff. Without a decent niche that you are capable of working you are screwed no matter what your PPC budget is, no matter how good your content writers are etc.
Some very general approaches worth considering:
1) Build around the offer -- ie. find a good CPA offer and build PPC campaigns, content sites etc. around it the offer. Start small, and if it's generating income scale "up" (more sites, blogs, PPC etc. around the same offer.) If it's generating lots of traffic but few conversions scale "out" (ie. find new offers to target with the existing sites, blogs, campaigns etc.)
2) Search trends -- various types of search analysis sites are out there, such as Google Trends. Find topics that are building in popularity, build around them and find monetisation strategies that complement your site.
3) If you are into promoting specific products, use the many shopping sites out there, including eBay's Want it Now, Pulse and What's Hot sections, Amazon's best seller ratings, Shopping.com, TheThingsIWant.com etc. etc. etc. to find out what products are getting tons of buzz right now. find a decent affiliate program, crank out review sites, PPC etc. and just move from product to product as the market's tastes change.
4) If you're proficient at writing or just in love with the concept of article marketing, focus on tutorials, tech and "how to ..." content. It's easy to find inspiration for what topics to hit at Yahoo Answers, Google Answers, 43Things.com, eHow, About.com etc. as all of these sites track popularity of various topics -- I like to look at 43Things.com for example and compare the top "declared" goals to the top "accomplished" ones. The ones that are declared but not accomplished are good potential markets to look into for content geared towards teaching people how to do it, motivating them, starting a discussion forum geared towards those kinds of users etc.
5) Seasonal niches -- I know a few people who work entirely around short life span stuff that comes around each year; eg holiday-specific shopping ("Christmas ornaments" not "Christmas presents for Dad") , sports schedules and that kind of thing. Properly planned these can be great, the money is fast and if you do well each year you have a more solid base than the previous on which to build.
Once you have a general niche, you need to dig into the search engines and kw tools to find how much volume and for what phrases that niche is really getting, before you go spending any serious money trying to market it. This is deeper research and a whole other topic itself, so I'll leave it off for now; hopefully the above at least gives you some ideas about how to go about looking for a starting point.
Frank
