This is actually an ADO/ADO.NET tip and it applies to other database systems as well.
I can code basic connection strings by heart, but anytime I need to do something fancy or access something other than SQL Server, I use ConnectionStrings.com as a resource. It pretty much covers every combination of a database system and a data access API under the sun. There are some databases listed I've never even heard of, like Mimer SQL. The SQL Server section also includes some additional stuff, like specifying the network protocol and all connection strings properties.
The best thing is that the URL is so intuitive, you don't even need to bookmark it.