Just released SharePoint SDKs; these look quite meaty -- The wss one weights in at nearly 34MB, compressed.

Windows SharePoint Services V3: SDK

This SDK contains conceptual overviews, programming tasks, samples, and references to guide you in developing solutions based on Microsoft® Windows® SharePoint® Services (version 3).
 
SharePoint Server 2007: SDK

The Microsoft Office SharePoint Server 2007 (Beta) SDK contains conceptual overviews, programming tasks, code samples, and references to guide you in developing solutions based on Microsoft® Office SharePoint® Server 2007.
 

Hmm, I just realised that RC1 and RC1 Refresh have different build numbers and are not binary compatible. Here's another drop built for rc1 refresh, 1.0.9567.0:

(old binary removed) - latest version always at:
http://www.codeplex.com/PSSharePoint

I've got the bones of a Compressed Folder (think zip files) provider lying around, and I was wondering if people would be interested to see a blog entry on how to put it together? I think I need a bit of a break from the SharePoint provider, so I'd be happy to write up a two-parter on how to get it up and running. Everyone seems obsessed with cmdlets; has anyone else got the psprovider bug, or is the learning curve too steep/documentation too confusing?