The following is a jumbled list of things to keep in mind when optimizing websites: HTTP Server Configuration

• On HTTP Compression
• See the HTML5 boilerplate .htaccess file

Free Web Server Performance Scanning Services

• GTmetrix cleanly shows areas of improvement, grades, and offers detailed suggestions for improvement based on your code.
• PingDom offers a free slick website performance analysis tool
• Web Page Test gives a detailed list, waterfall charts, and a nice summary of your server's performance
• Google Page Speed Insights provides a list of issues and remedies. It also provides a separate performance score for mobile and desktop
• MXtoolbox will check your server for multiple web/mail/dns issues

Use a fast VPS:

• Digital Ocean
• Server Bear offers a great way to search VPS offerings, filtering on your own criteria

Use a CDN:

• Soft Layer/Edgecast
• CDN Planet reviews many CDNs and allows you to compare any two

Use a fast DNS server:

• NameCheap is an efficient and popular service that's quite affordable
• DNS Comparison compares 10 of the more popular managed DNS services
• DNS Reviews talks about all the various DNS performance issues and provides response time list that's updated daily
• CloudHarmony has an independent review of some of the top managed DNS providers
• CatchPoint has a blog talking about some DNS options
• Amazon Route 53 is a fast and affordable managed DNS solution. Their cheapest offering works out to $1/month.