Currently, IBM, Hewlett-Packard and Dell sell the most servers, in general, and the same goes for blades. But don't disregard blades from smaller vendors, who may be able to help you provide more personal service and customization.
No industry standards for blade servers exist at this time, making it tricky to choose the best hardware. Most likely you'll help your customers choose one vendor to work with, just be sure the vendor offers the price and warranties desired.
Blade servers come at various prices, numbers of blades per unit, warranties, etc. Some will come with a Linux operating system distribution pre-installed.
Choosing a Linux operating system distribution
You and your customers have no shortage of Linux distribution options – but that will also complicate your decision. Consider if you want to offer your own support or use the support provided by the Linux distribution, if available, and if it's free or not.
For instance, Debian and Gentoo are two distributions with no professional support readily available, but do offer robust communities and a few specialists.
Since you're looking for a Linux distribution to run on a blade server, you don't want to pick one that's tailored to desktops. Look for server-specific installations.
SLES 10 and RHEL 4 seem are both optimizing for 64-bit systems and making alliances with HP, IBM and Dell.
Free versions of Red Hat, SUSE or other distributions may work for smaller installations.
Get additional considerations in choosing a Linux distribution to run on 64-bit blades at SearchOpenSource.com.