Drupal websites can benefit from a little bit of care and attention to fine tune their performance. Here are some tips for how to speed up your page loads.
Advagg - advanced aggregation
Varnish - http cache
Varnish is a web application accelerator, basically a server-side caching system. It sits in front of your webserver and checks every request to see if it can serve up a cached version, which can be served much faster by Varnish compared to asking the web server to make the round trip to the database. Because it keeps traffic away from querying the database it also reduces the load on the processor, which can also help to speed up your site.
CDN - Content delivery network
Again this is something which reduces the load on the web server and outsources it to a third party. In the case of a CDN, assets such as images, files and scripts can be served from a location close to the end user, the result is faster page loads and reduced server load. The down side is the additional cost of the CDN.
Honeypot - httpbl
Project honeypot gathers information about content spammers and uses this to block IP addresses of known spammers from your site. Users around the world set up honeypots - hidden scripts, invisible to real users but irresistible to spam bots - and feed the information about spammers IP addresses back to project Honeypot. The end result is fewer page views going to spam users and more cpu, memory and bandwidth available to your genuine visitors. It's a really great collaborative effort to thwart the bad guys.
Another way to speed up your site is to make sure the images on the page are as small as possible. The Imagecache module is a good start but you should also think about using responsive images and lazyloader to only load the visible parts of the site. It might also be possible to optimize images before they are uploaded if the site is displaying original images in any slots. Use posterize on images with flat areas of colour to reduce size before you save them out. You can read more here about how to resize images for your website.
So, that's five useful things you can do to tune your site. Not all of these techniques will be appropriate for all sites and each site poses its own unique challenges, but these 5 techniques are a good start for fine tuning your site and enhancing the experience for visitors to your web site.