Hmm, I wouldn't go for adsense ads.
First of all like John said, you only make a couple of cents per click with most keywords and those keywords that pay out well are very hard to bring traffic to because you compete with so many other webmasters.
If somebody clicks on your ads, that means this person is interested in what is advertised there, so you could as well make this sale for your affiliate products rather than sending this visitor to a different site where he makes a purchase.
Finally you never know for how long you are going to have your adsense account, mine got closed without me doing anything wrong and google stole all my commissions. That wasn't the worst, I had to update all my websites and place different ads there, which took me hours.
You should rather sell clickbank or commission junction affiliate products, you will earn a lot more on the long run. Combine this with a newsletter on your site to build up trust with your visitors and you will even make more sales.
Be aware that the old static html websites will only earn you pennies, maybe you make it to $10 or $20 a month with such a website but more is almost impossible. That's why those adsense marketers have hundreds of those niche websites.
You should build a dynamic Web 2.0 website with a forum and other interactive features, that will result in more visitors and more income. If you build something unique, that can not be found anywhere else, then you will have a winner website and you won't need to advertise it at all, it will spread like a virus through mouth to mouth propaganda.
For me personally, I concentrate now on creating membershp websites and on building my opt-in email lists. My niche websites, like the cat website were never a real success, although I worked a lot on these. But they still make me a couple of bucks each month without me doing anything, so I guess I would be a rich man if I had 300 of these

Guido