I have so far found two online sites that I have been able to make/reclaim money from.
Gomez Peer Zone
The website gives you a good overview of the ins and outs, but essentially you get paid for running a piece of software on your PC in the background. The software benchmarks a whole bunch of URLs based on your internet connection and location, and in turn you get paid per minute of processing time.
You can earn up to $45 per month once you become "activated"; this took me in the region of 180 days since they assess new clients for activation based on demand and existing clients in your area. I leave my PC on 24/7 and get just over 10% processing time, so average in the region of $7-8 per month at present, which will vary for you. This hardly covers the electricity cost of leaving my PC on, but I leave it on for other uses anyway :-)
I believe this is for UK residents only at present; I am sorry if this does not apply to you!
Once again, the website explains all of the details better than I can, but in essence you earn cashback from lots of popular online retailers if you load their site up through Quidco. The amounts typically range from 1% - 10% (sometimes a lot more!) and get paid a few months after the transaction completes successfully.
I use this for virtually all of my online shopping, insurance policies, breakdown cover and such like. It takes less than 30 seconds to get to the retailers website through Quidco, and there is a handy totaliser to let you know how much you have saved. Money gets paid directly into your bank account every month, so long as you accrue over £1. I have been a member for around 2 years and have been paid £861.88 which would have otherwise gone to the retailer. (This of course means I have spent a FORTUNE online, which perhaps explains why my salary seems to disappear quickly each month...).
So why not give it a go?