Open source solutions for a grid infrastructure?

I've been searching for the last few days for any open source tools that could help in building an infrastructure for deploying grid or utility computing services. I haven't found anything yet that does everything, but maybe it is out there.

The AppLogic product by 3Tera looks pretty cool. It uses a combination of open source and proprietary technologies, including Xen and NBD. Hosted solutions can be purchased directly from 3tera, or from Layered Technologies (thegridlayer.com) and FortressITX. I can't tell, but I think that SoftLayer may host some grids, but they may not sell the service.

My initial thoughts would be to build an IP SAN across the servers using DRBD, LVM, and GNBD. This page at gridvm.org has a good description of doing this (in fact, I should read everything on the gridvm.org site):
http://www.gridvm.org/drbd-lvm-gnbd-and-xen-for-free-and-reliable-san.html

This is where I then get fuzzy on what would need to go on next. I'm assuming Xen would be part of it, but I don't know how to make one application span over multiple servers. Need some sort of grid layer?

Maybe the AppLogic approach doesn't let a single appliance within an application span over multiple servers? Can scale to use all the CPUs on a single server, but not more than those in a single server? Not sure, need to look into this.

There is tremendous value in the AppLogic product's web based front end and CLI tools. These tools seem to be spectacular. Obviously, building a solution with OS products would not have that front-end.

I should also look into Virtual Workspaces and see what it is all about:
http://workspace.globus.org/index.html

Edit 10/7/2007:
Another player in this realm seems to be MediaTemple. Their system doesn't look nearly as sophisticated as AppLogic:
http://www.mediatemple.net/webhosting/gs/