How to display content from a second database
Maybe consider the Forena module for accessing your data in your custom database. It seems like a perfect fit for what you're asking for. It also includes charting features, which is typically a related requirement. Not many people know about it, which is why I wanted to mention it here.

Forena is built of the idea of using SQL to get data out of a database and use XHTML and CSS to format it into web reports. 

Various DBMSs are supported, such as Oracle, MS Sql, Postgress, SQLite, MySQL, any PDO compliant DBMS. You didn't specify if your custom database is any of those, but any of these will do ... And there are quite some reasons for considering Forena.

Visit the Forena HowTos page for some links (near the bottom) to some live demo / showcase links.

Note: I'm a co-maintainer of Forena.