I’ll be doing some more research on this before recommending it for specific projects, but Microsoft now offers a free database server: SQL Server 2005 Express Edition. Basically, it’s a free version of SQL Server that’s redistributable and can be used in a production environment (unlike their earlier, free-ish SQL Server 2000 Developer Edition). There are some functionality limitations, including a 4-gig database size limit. But frankly, I haven’t worked on a web project yet that would have exceeded that limit. Obviously this is something Microsoft has developed under mounting pressure from MySQL and Oracle’s freebie version.
However, having played around with the full version of SQL Server 2005 a bit, I have to warn you there is significant culture shock moving from SQL Server 2000–it’s not trivial to translate databases (or DBA skills for that matter) between the two. And having recently implemented a MySQL database for a remote production environment, I can say that the stability, functionality and manageability of the most recent MySQL release almost makes SQL Server moot for small-scale projects. Still, something to keep an eye on.