I'm writing today about a hefty and beefy server called the PowerEdge T710 from Dell. This is a server that's available as a tower or as a 5U rack mount, and if you have the hardware you can easily convert it from one to the other.
This is a dual processor system, able to take Intel 5500 and 5600 series CPUs, with four or six cores. It will run fine on one CPU, if you want a more affordable starting point, and adding a second CPU is a simple manner, giving you some room to grow.
Speaking of room to grow, the T710 has eighteen slots for DDR3 RAM. You can put in 1GB, 2, 4, 8, or 16GB sticks in various configurations, with a maximum of 192GB of RAM support, making it very useful for running a bucketload of virtual machines.
For more permanent storage, the T710 is available with either eight 3.5” hot sway drive bays, or sixteen 2.5” bays, accepting SAS, SATA, or even solid-state drives. To control these drives, you can use a controller such as a PERC6i, H200, or H700 among others. The different cards give you different options of having battery backup with cache, not having it, having different sized cache and so on. There are two options using software implemented RAID control, the S100 and S300, but these will only work with a Windows OS, such as Windows Server 2012, Windows Server 2008 and so on. If you want to run Linux, you'll need to avoid the S100 and S300.
For remote access and control of the system, you have the option of the iDRAC6 Express or the Enterprise version. The regular Express provides remote management and monitoring over a network, with web and CLI interface options. The Enterprise boldly goes where, no, wait. That's not right. The iDRAC6 Enterprise provides the same functions as the Express, but also has a dedicated NIC port for remote access, as well as having a slot to use Dell vFlash Media card which enables Dell's Virtual Flash system. Virtual Flash lets you have diagnostic images, system recovery, emergency boot images and other tools, independent of the system's hard drives.
You can run this with one hot swap power supply, or if you want the security of redundant power, you can use two power supplies.