I am designing a site with a javascript login that leads you to a flash actionscript site.
What language would I be looking at for a database? Mysql? I can use any feedback.

You can connect from JavaScript to database, and validate user credentials, if has permission you can from JavaScript redirect him to the Flash page!

thank you; however I am not sure what database language I should use.

Database language or Database software?
Database language would be mainly ANSI-SQL and you can use Microsoft Access or Microsoft SQL Server.

MySQL is easier to find online on most hosts.
MS Access requires MS server and costs more to host.
MySQL is free

MySQL free means they also most likely have PHP, which some Windows boxed server providers still dont like to support for some reason.

PHP login is faster and safer than Javascript.
You can still detect if the user has JS capabilities but provide better security using PHP to hold the login data and expirations.

MySQL also permits one-way passwords without external encryption and even if you build this yourself it could be done in a matter of a few hours.

Access has limited support on other O/S and max 2 GB database or table size.

MS SQL on 32 bit O/S is also max 2 - 4 GB scale when it grows

MySQL limit is 14 TerraByte and scalable beyond this limit in clustered networks.

It all depends what you want to do in the future when your site grows.