I have been wanting to mess around with VistaDB for a couple of projects, and have been waiting for all the .NET 2.0 associated releases.  I liked some of what SQL Express had to offer (Eric Kepes gave a great presnetation at BADNUG not too long ago), and I've found some small good in Firebird SQL, but not enough to make that part of my apps.  A lighter DB along the lines of Firebird SQL but meant for .NET is very appealing.

Here's their official announcement (check out the cool offer at the end):

VistaDB 2.1 database for .NET has been released
This 2.1 update includes over 60 improvements, including new support for .NET 2.0 and Visual Studio .NET 2005. VistaDB is a small-footprint, embedded SQL database alternative to Jet/Access, MSDE and SQL Server Express 2005 that enables developers to build .NET 1.1 and .NET 2.0 applications. Features SQL-92 support, small 500KB embedded footprint, free 2-User VistaDB Server for remote TCP/IP data access, royalty free distribution for both embedded and server, Copy 'n Go! deployment, managed ADO.NET Provider, data management and data migration tools. Free trial is available for download.
- Learn more about VistaDB
- Repost this to your blog and receive a FREE copy of VistaDB 2.1!

There are a couple tweaks you might need to know about if you use VS 2005, read more at http://www.vistadb.net/news_051101_vistadb211.asp.