You can also test out a kw to see if it's profitable without putting up an actual site... Here's how...
Pick the most competitive kw phrase and write a "blog post" but don't post it to a blog. Sounds weird right?
Then change it to a press release format - something like I've done here in the attachment below... you'll see I've targeted a VERY competitive keyword, "seo software".
I know there's nothing new about press releases, but they work if you do it right - but only for a short period of time, usually if it gets picked up by google news it will last up to a few days on Google's page 1 (and you'll probably get some people linking their tweets to it).
As you can see, just base your press release off of the sales page you are sending your traffic to, and your writing efforts will become much easier
You can do this for free if spending a small amount of money is holding you back.
Here's some free press release sites for you:
PHP:
hxxp://www.release-news.com/
hxxp://www.jazzou.com/
hxxp://www.pressabout.com/
hxxp://www.sanepr.com
hxxp://www.bignews.biz
hxxp://www.prlog.org/
hxxp://www.boosharticles.com/
hxxp://www.fgnpr.com
hxxp://www.booshplr.com
Of course, this is not a niche I would go after or compete with and build a site around because of the huge competition, but my point is... before you go after something, be sure it's profitable with a test, and just try it out if you are not sure because there ARE other ways to monetize even the most competitive of keywords
Oh, and yes, I did make a modest amount of commissions with that press release in that super competitive kw phrase - for about an hour's worth of work... so feel free to copy/modify whatever... just be sure to submit different variations of your version to the different sites
