A very stable and solid distro is the CentOS, which is exactly (more or less) Red Hat Enterprise Server. [centos.org...]
The default server install for CentOS 4.x will give you apache2 + php5 + mysql, if you pick those options. The install process is pretty solid and understandable. Lots of support on the web for it and I've always been able to find my answers via google.
For the more adventurous, I would also recommend Ubuntu 6. Very good desktop and server, with a growing community and pretty slick apps installed.