A free tool for managing your MSDE or SQL Server (MSSQL) databases:
It does most stuff relatively well. Add/remove database, attach/detach, browse data. Unfortunately, no visual view builder. It's not quite as capable as the SQL administrative tools included by Microsoft with SQL Server, but it's sufficient. And the price of 0 is good.
Another freeware MSDE manager:
Microsoft, themselves, provides a Web interface (which can run locally with an included mini-web server):