SnapFiles a good one-stop-shop for free and open source software neatly organized into categories. Another excellent source is FileHippo which offers the bonus feature of alerting you when new versions of your downloaded software become available.
This is a good source for viewing browser type usage statistics over time.
This is a good resource for jumpstarting your CSS design. This is a blend of CSS2 and CSS3 resources. I have not worked with these but they are worth checking out.