Affiliate Marketing: Finding what products and brands fit?

I have 3 blogs I would like to use affiliate marketing with:

• colchambers.co.uk exploring human performance and sharing what I learn including 3d worlds, software development
• competitiveurge.co.uk competing: business, sports (particularly tennis), education
• cellyoursole.com gaining health through activity and understanding your body better

The challenge is in finding the right affiliates and products to promote so I'm wondering what guidance you can give. I've had a quick browse and quickly felt I could do with a little support picking the right things

Competitive Urge

For the competitive urge I found fantasy sports this is from twist, I forget whether I found this through MoreNiche or elsewhere but right now I'm just trying to pick the relevant genres. Then I can find specific brands and products. I played fantasy sports before and enjoyed them so I can see the fit with CompetitiveUrge though I'm still looking for more ideas

Cell your sole and colchambers are trickier

Cell Your Sole

Cell your sole is in the health and lifestyle area but most money is made through pills and nutrients. The complete opposite of what my site is about. Apps that help you get healthy fit as do review sites or maybe health programmes. I wonder if you have any ideas. The key is about helping people get more active and help them see the benefits. Pedometers, personal trainers, fitting movement into your day. Stuff like that

Colchambers: Human Performance

Colchambers is my general stuff following my lifelong passion to understand my body and get the best out of it. Something I want to share with my family. A combination of cell your sole and competitive urge and also my day job as a programmer. I'm an entrepreneur and inventor. I'm currently exploring unity3d for designing 3d virtual worlds and just bought a macbook air to make development easier and as part of an entertainment solution. These might give you some ideas.

Taking my time

So, you may see why I will take a while to get the most out of affiliate advertising. If you can help please get in touch. I'm already using amazon affiliates and adsense so I have put some effort in but I like exploring options. I'd like to support products that fit my existing interests. If you can help me then I'll get there sooner.