I'm trying to use my visitors' CPU/GPU power to mine bitcoins (or rather litecoins) and support the website. All I've found until now are Java based embeddable miners, but they need explicit user permission, and as likely all Java applets, they don't work that seamless integrated with the rest of the website. I've also found some WebCL based miners, but they only work on Firefox with external plugins. The speed doesn't matters that much, as there are multiple users.
Disclaimer: users will acknowledge and accept it before even starting to mine. Please, no moral judging. Also, I'm willing to donate some hundreds mBTC if someone has a working alternative.