If they're low-traffic just run apache

, it's in every package manager so it is updated. It'll run just fine on a Linode 360. With CentOS, the main downside may be that you get php 5.1.6 instead of php 5.2. Ubuntu would have more packages--it has nginx too, but it's an older version than the current.
Really, I would stick with your distribution's packages. It's all tested together, it's super easy to install and update, and chances are there is documentation.
If you do compile anything from source just sign up for that software's announcement list so you know when there is a bugfix or update.
For mail, exim and postfix are good and you can get tutorials for either. I've used courier-imap a bunch for POP3/IMAP service.
If you have room on your linode for a different profile and disk images--try Ubuntu. Switching is pretty easy and the versions of things will feel more like Fedora compared with CentOS.
Edit: You don't need to run httpd. Just chkconfig httpd off, and configure nginx appropriately.