Gerber2PDF is a command-line tool to convert Gerber files to PDF for proofing and hobbyist printing purposes.
It converts multiple Gerber files at once, placing the resulting layers each on it's own page within the PDF. Each layer has a PDF bookmark for easy reference.
Layers can optionally be combined onto a single page and rendered with custom colours and transparency.
There is a Drill to Gerber converter available from the downloads page.