motherboards to buy now for desktops, vendors?

[Greg Troxel <gdt%ir.bbn.com@localhost>]

We need to get some more desktopish boxes, some of which will be xen
servers, but are finding lots of motherboards with 82566 chips which
NetBSD seems not to support (but see
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/dev/em/if_em.c
for a FreeBSD driver).

What I'm looking for is

  high-quality system: cost is much less important than having no grief

  i386/amd64 dual-mode processor

  can take 4G ram, preferably more

  runs NetBSD fine (/i386 and /amd64) and runs xen3 fine

    x on builtin graphics a big plus (or no builtin and enough slots)
    working builtin network a big plus (or no builtin and slots)
    SATA disks work flawlessly
    no issues with usb/etc.
    sound ought to work, but perhaps not critical

And, I would want to know a place that would assemble these with Lian-Li
PC-60 cases, or some other quiet high-end case for desktop rather than
xen box usage.

It looks like Intel 975X motherboards are still available, and we have
one of those that works fine.  So perhaps we should get more of those.

Any clues would be appreciated.