Generator Studio is a code generation tool (yes, another one one, but more on that later) that allows you to set up templates using the Velocity Template Language, and then generates files based on your source database structure. It can be found here on CodePlex and the Pre-Beta 0.1 can be downloaded here
WARNING: It's very beta. Its generates well (we think), but we have a host of features/fixes that we'd like to add in the future. At present, it's being contributed to by FryHard (a.k.a. Brendan Fry) and I, and we tackle it in our spare time.Top of our list is to tidy up the UI side, and implement ALL of the sql calls using NHibernate/ActiveRecord. You may notice some inline SQL statements that, at present, I haven't managed to work around (mostly because of time constraints :)).
Why another generator application? I agree fully with the thoughts around the "Reinventing-the-wheel" anti-pattern - developing something that is already out there, but you don't like it because you didn't write it, is stoopid. BUT. I started this many years back in some-or-other form, and in recent times I've struggled to find an open-source project the generates what I want. So here it is.
Use it. Don't use it. Send us templates. Check back here/codeplex to find new templates.
UPDATE: 2008 NOV 03 4 extra templates have been added to the source - 2 for creating audit tables for your database (one style using a GUID as the PK for the audit tables, the other using an identity column) and the other two for generating the corresponding triggers to populate these tables.