I recommend the W3 Total Cache plugin: http://wordpress.org/extend/plugins/w3-total-cache/
You can use it to generate static HTML pages of any part of your site, which can then be served to your users, thus dramatically decreasing load time.
If your site has enough users to warrant using a CDN, this plugin will help you with that, too.
And the best part ... it's free!
Apart from that jQuery Image Lazy Load WP, might be worth a look: http://wordpress.org/extend/plugins/jquery-image-lazy-loading/
This ensures that images on your site aren't loaded till the user needs them.
Hope that helps.