a good SCSI Ultra320 32bit controller

i could not find any controller on newegg, i'm interested in something 32bit PCI but with Ultra320 standard.

Most of the 64/66 PCI and PCI-X controllers are backwards compatible to 32/33 PCI. It's not hard to find those, but another question is will you be running enough drives to need a U320 controller? U320 for lower numbers of drives has extremely limited benefits, since the drives are still the bottleneck. Since you have no access to a faster bus, about 110MB/s is the maximum bandwidth for most PCI bus architectures and saturating a U160 channel will not be possible. A much less expensive solution will be to use an entry level card, like the LSIU160, usually about 40.00 shipped at Newegg.

ok, but will that controller support an 15k rpm ultra320 drive and offer reasonably better performance than SATA drives at the same time?
i was thinking about getting one of the famous 36.7GB 15k rpm Fujitsu MASxxxx drive....

Yes, I've run MAS and many other drives on them without issues and it is less expensive than many of the other alternatives. On the performance side, expect STRs in the mid to high 70MB/s range, very similar to the 74GB Raptors. Where the drives really shine is the access time and firmware optimization for multitasking and high levels of disk IO. The access time does give a more responsive feel to the OS and applications, especially with multiple processes. As to whether you'd find it better performing, it all depends on what you do most. If you tend to do multiple high IO tasks, then this is the way to go. For a normal use or gaming box, this is probably overkill and a 74GB Raptor will be a better cost to benefit ratio.

Is a U320 controller (onboard or expansion card) backwards compatible with U160 drives? Are they the same pin layout or would one need an adapter?

They are backwards compatible with any LVD drive. LVD drives will also run at their rated speeds if combined. This means that you can run mixed U2W(80MB/s), U160 and U320 drives and they will all burst at their rated speeds. This will limit burst tramsmissions to the highest rate of the controller.

The 68pin cabling is standard. Backplanes, SCA hot swap racks and other connections may use prooprietary connections provided with the unit. Adapters are available for SCA to 68pin, but usage should be limited to no more than three per channel, due to capacitative inductance interfering with signal quality.