Best for what? A Sun Ultra 40 M2 workstation is pretty good, and comes pre-installed with Linux or Solaris.
Sun Ultra 40 M2 Workstation
2 Dual-Core AMD Opteron Model 2218 Processors
1 MB On Chip L2 Cache per Core
16 GB (4 x 4 GB DIMMs) Registered DDR-667 ECC Memory
1 x 250 GB 7200 rpm SATA Disk Drive
1 NVIDIA Quadro FX 5500 PCI-E Graphics Card
1 DVD Dual (DVD-ROM and CD-RW Combo)
2 x 10/100/1000 Ethernet Ports
8 USB Ports
2 IEEE 1394a Ports
2 PCI-Express x16 Slots
2 PCI-Express x8 Slots
1 Conventional PCI Slot
Sun Studio Software Preinstalled
Sun Java Studio Creator Software Preinstalled
Sun Java Studio Enterprise Software Preinstalled
NetBeans Software Preinstalled
Sun N1 Grid Engine License Included
Solaris 10 Operating System Preinstalled
3 Year Warranty, 3 Year Parts Exchange, Next Business Day
http://shop.sun.com/is-bin/INTERSHOP.enfinity/WFS/Sun_NorthAmerica-Sun_Store_US-Site/en_US/-/USD/ViewConfigurations-List;pgid=1RaQnB4nsPlSR0ISfAnMSxKc00007uu2GVGi;sid=SEbrPKLReXzrOOTsbzOjOU1P_cTJ1OEbGkeqcrgsaKT4lg==?ProxyProductRefID=DUMMY3--Sun_Ultra_40_Workst@Sun_NorthAmerica-Sun_Store_US&CatalogCategoryID=VBJIBe.heFkAAAERyjcuhFdb&ShowAllProducts=false