There are plenty of useful sites for Factors Affecting and Improving Performance that I use all the time. They provide up-to-date information and cover lots of content.
Possibly the best of the useful sites for Factors Affecting and Improving Performance resource online for FAP and IP is the Strength and Conditioning Research website. This website contains a mountain of information on the various types of training, periodisation, nutrition and more. The easiest way to find something is to search for it and look through what comes up. All this information is current research and very useful for looking at training and performance.
The Australian Institute of Sport (AIS) also provide some useful information. The site can be hard to navigate, so I often search through Google and limit my finding to www.ausport.gov.au. They have information on nutrition and technology along with plenty of other relevant information.
Others
Sports Dietitians Australia (SDA) also provide plenty of useful content related to sports nutrition. Of particular use are their factsheets and blog. Adding to our list of useful sites for Factors Affecting and Improving Performance is the Australian Sports Anti-Doping Authority (ASADA) and the World Anti-Doping Agency (WADA) both providing plenty of information around the use of drugs in sport.