Mac Pros, which run certified Unix (OS X) are possibly the _best_ option for serious professionals.
Who cares whether a Unix is certified? Linux is the big daddy of the server rhythm these days. It's all been over but the tears for Big Iron Unix since you started seeing people consider the GNU toolchain 'indispensable' on it.
There are also a couple other companies making one or two choices in well-built hardware you can install enterprise Linux on, of course.
There's a lot of companies making much more capable hardware these days, particularly in the graphics department, and featuring considerably more expandability. Much of it comes at significantly lower cost, as well, and if you spend more money, you'll know what you got for it in most cases.