apt-get install everything.
Debian is very good at keeping its packages up to date, as far as security is concerned. It won't get you the latest features (so the version numbers might look old), but every security fix is back-ported to the versions that Debian maintains. For example, Debian's PHP is 5.3.3, but it contains all security fixes from 5.3.10. Popular packages such as Apache and PHP are usually patched in a matter of hours.
If you need newer features,
dotdeb is an excellent source of up-to-date packages for Debian. Dotdeb also gets security fixes very quickly, and it integrates seamlessly with the rest of Debian's update mechanism.