Then either get an HP Proliant like Visvanath mentioned, or Dell Optiplex will do as well, or best off built one yourself, get a Super Micro Motherboard for AMD Opetron 6272, its 16-core CPU will cost you as same as buying a XEON with 6 core, cheap and simple.
in either case, dont get a rack unit design, they are noisy and more expensive, just get a tower chassis.
and last and not least, though I had mentioned that before too, and Howard just mentioned that am I am tripling on that, a separate system is a separate system, where Database gets most punished, so putting it on independent machine would make a difference.
Just to let you know, rather getting a 8-core and 16GB Ram server, (or) alternatively getting 2 servers with 4 core and 8GB RAM each (though price will be higher too) but you'll get nearly twice the power of what you can get from a single box.