Luca wrote a step-by-step guide to Seeed Studio’s Fusion PCB service. It covers how to export files from Eagle and get your PCB built. It’s available both in English and Italian.
We like Fusion PCB service, it’s cheap and pretty fast. It starts at $10 for 10 PCBs ($1 per board), plus a few bucks of shipping. We’re biased though, so take our recommendation with a grain of salt.
A guide to Seeed Studio’s Fusion PCB service - [Link]