Sun has always been in the supercomputers list, but never particularily high up. I think this is mainly due to the historical cost of Sun kit, and because those that did have Sun powered supercomputers, didn't want to advertise the fact (I certainly wouldn't want my easily swappable and expensive CPU and memory boards knicked in the middle of the night).
Well, that's all about to change - the National Science Foundation has awarded the Texas Advanced Computing Center (TACC) $59 million for a new supercomputer.
From the press release:
TACC is partnering with Sun Microsystems to deploy a supercomputer system specifically developed to support very large science and engineering computing requirements. In its final configuration in 2007, the supercomputer will have a peak performance in excess of 420 trillion floating point operations per second (teraflops), making it one of the most powerful supercomputer systems in the world. It will also provide over 100 trillion bytes (terabytes) of memory and 1.7 quadrillion bytes (petabytes) of disk storage. The system is based on Sun Fire(TM) x64 (x86, 64-bit) servers and Sun StorageTek(TM) disk and tape storage technologies, and will use AMD's forthcoming quad-core processors.
420 teraflops would make this the most powerful supercomputer by a long shot - IBM's BlueGene/L recently topped the current Top 500 list clocking in at only 280 teraflops.
That is also assuming IBM don't upgrade BlueGene or another supercomputer appears on the scene between now and then.