QLogic has posted some info on the SANbox 9000 Series of high-density switches. This switch, which has been qualified for use with Xsan, can squeeze 128 4Gbps ports in its 4U chassis. Other blades are available to provide iSCSI, FC-IP or 10Gb FC. For really dense cores, you can use QLogic's 800 Gbps HyperStack interconnect between two 9000 switches.
They have an really useful faq that I found invaluable for presales engineering. For example, they are very upfront about current capabilities and limitations of redundant controllers. Also, QLogic has switched from XPAK ISLs to X2 ISLs (but there is a cable available to convert). Get past the salesy first page for the better stuff later on.