Yahoo has a tool called: YSlow. You can use it to pinpoint what optimisations you need. Install it as a firefox add-on. Also, have a look at their best practices listed for speeding up your website. It's a bit technical, but it is very good advice you should consider. It's worth skimming through. Hope that helps...
To be honest, there is much more to get a fast loading speed. It begins with the html code and ends with a CDN or cookieless domain. It takes hours to implement everything. I did that for all my websites and I am still doing it. I could easily make a service out of it and offer it for 49USD or more... 1. Analyzing the website 2. Generate detailed report 3. Choose the right "tactic" for your website/blog/cms 4. Recode parts of the website 5. ... 6. 7. Minimum 7 parts have to be done to get the best result. Just "remove unwanted JS script and use sprite image format" is NOT enough. You need MORE technical skill to get the maximum. Your webserver itself has to be tweaked too. All our Apache servers are tweaked, we have 3 dedicated servers in germany. You need to know A LOT to get the BEST results. --- And please, do not tell me "use nginx" ... that is NOT the solution, believe me!!! I can prove it, no problem.