Company Q3/2006
Revenue (million US$)
Market Share
IBM 4,381 33.7 %
Hewlett-Packard (HP) 3,290 25.3 %
Dell 1,406 10.8 %
Sun 1,314 10.1%
Fujitsu and Fujitsu Siemens (FSC) 634 4.9 %
Others 1,988 15.3 %
Source: Gartner (11-2006)

IMHO, choosing the right server company will ensure better supports, in terms of hardware, driver and service. Although price wise might be higher than lesser known companies, but in long term, you might save more.

The Server Primer, Part 2 | Tom’s Hardware: