I would be careful with phpthumbof as the more work you have it do the more intensive it can be on the server (which slows things down). That's not to say it's a bad thing just be careful when using it.
Compression Continued
On the other hand you can also reduce filesizes using GZIP for faster transfer:
<ifmodule mod_deflate.c>
AddOutputFilterByType DEFLATE text/text text/html text/plain text/xml text/css application/x-javascript application/javascript text/javascript
</ifmodule>
If you have locally hosted webfonts you could do (webfonts only):
<ifmodule mod_deflate.c>
<ifmodule mod_mime.c> #Checks if your server supports Addtype
Addtype font/opentype .otf
Addtype font/eot .eot
Addtype font/truetype .ttf
</ifmodule>
AddOutputFilterByType DEFLATE font/opentype font/truetype font/eot
</ifmodule>
Putting it all together you can use it on everything:
<ifmodule mod_deflate.c>
<ifmodule mod_mime.c> #Checks if your server supports Addtype
Addtype font/opentype .otf
Addtype font/eot .eot
Addtype font/truetype .ttf
</ifmodule>
AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css application/x-javascript application/javascript text/text font/opentype font/truetype font/eot
</ifmodule>
Additionally you can include images to save even more, however the server will take more of a hit generating the compressed files.
Offloading Common Files
Another secret to speeding your website is using JS CDN Libraries, such as the popular Google Hosted Libraries (
https://developers.google.com/speed/libraries/). The slightly less common library, but actually faster (in my limited testing) is the one run by CloudFlare (
http://cdnjs.com/) and this one has the added benefit of including more files! So you can offload more than just jQuery and such. Heck they even have some of the common css libraries (960gs or 1140 anyone?)
Avoid Blocking
If you have a lot of resources on your site (css, js, img, etc) you will also run into a blocking issue. Basically you need to wait for other resources to download before downloading even more resources. You can counter this issue by using alternative addresses, and stagger their usage.
You could setup four subdomains (static, img1, img2, img3) all pointed to the assets folder. Once setup you would use ___.domain.com/images/____ or ___.domain.com/template/default/____ addresses (substituting your subdomain and the required file.
This allows your browser to download more files at the same time for a faster overall load time. Granted this does have it's downsides in that you are increasing http requests which does slow your load time some, so there are trade offs using this method.