If your site is hosted on a dedicated server and have some administrative skills.
Refer to Methods To Speed Up Magento .
1- Go to System->Configuration->Advanced and disable all the modules that your store does not use.
2- Use CloudFlare.com which seems to be a great free CDN service, it saves you some bandwidth charges and your site is more stable when it’s busy. The CloudFlare service improves your website’s performance and security by automatically caching static content on your website in multiple locations around the world and serving the location that is closest to your end-user.
3- Use different attribute sets for products using different attributes and only add attributes used by products to the attribute set.
more is coming - check it back later.