Some of the stuff I find handy...
* When ordering a Dell PowerEdge server, don't forget to buy the Enterprise DRAC and get it wired up. Provides a Web interface for the status of the machine, virtual media (yes, another way to install the OS without needing PXE boot) and, most importantly, a VNC terminal session to the main hardware (right from power up, BIOS, grub and the OS!).
* Install OMSA on PowerEdges, just for their "reboot recovery" option (if the kernel hangs, you can set it to wait so many seconds and then cold reboot the server).
* I like using rdist to keep customised system files synchronised across Linux servers and desktops. Think of it as a "networked make" utility and it's extremely handy once your server count gets into double figures.
* I use rsync to sync the system disk partition to another identical partition once a week via cron. In fact, it's a bit trickier than that (you have to change grub.conf and the copied /etc/fstab) so I've got a script to do it, but basically if I mess up the original system partition, I can boot into the second partition as an immediate rescue. Most useful if you run the sync script just before doing "yum update" (it allows you to roll back the update by rebooting into the pre-update partition).
* nagios for monitoring of course - install nrpe on the clients (yep, we rdist our custom config for nrpe) and then add the clients to the nagios server setup (we wrote a script for this part). With Dells that have OMSA installed, there's nagios modules to check OMSA info (e.g. temperature) and even some disk controller statuses.
* LDAP for authentication - quite tricky to setup, but useful when it's working properly. Don't forget to leave root as a local user in case the LDAP server goes titsup!
* amanda 3.X for tape (or even disk) backups. Amanda 2.X was dumb about autoloaders so we had to write a lot of custom wrapper scripts to check tape barcodes, load from autoloader, put back etc, but 3.X is actually good with autoloaders at long last. Now has (mostly) working Windows Amanda clients so we've even started backing up Windows clients too. Server-side encryption and compression are bonuses too (replace gzip with pigz in the Amanda server config if your tape server has many CPU cores).
* For VMs, we mostly use Proxmox VE in a clustered setup with KVM-based VMs (a mix of Windows and Linux clients). It's probably not as slick as VMware, but it's a *lot* cheaper! To be honest, I tried VMware a few years ago and couldn't believe it prompted you to rebuild kernel modules interactively as part of the boot sequence if you updated your kernel RPM and rebooted your VMware server. What if you didn't have console access at the time?! They've probably fixed this awfulness by now, but I couldn't believe how naff that was at the time.