Centos 4.x or 5.x is a great selection. I also agree with the above on choosing WHM/Cpanel as a control panel.

There are alot of people who say Plesk, and those under budget say Directadmin. I can assure you WHM/CPanel is more powerful and affordable (with Plesk you pay for plugins such as spamassasin and firewalls...) whereas WHM lets you integrate them for free.

REgards