I got my hands on the Synology DS1511 about year back now and its been operating very solidly this whole time and I love it, and now they have come up with their next iteration which I would recommend since its based on the same machine but with upgraded features. Other then the 5-bays, this NAS device sports some very cool feature set:

• USB 3.0
• User-replaceable fans
• Passive CPU cooling
• 2.13 GHz, dual-core CPU
• Up to 3GB of RAM
• High speed network transfers with link aggregation
• Support for emerging 4TB hard drives

The DS1512+ is the successor to the DS1511+ and is available starting today at a MSRP of $799.99. As with the DS1511+, the DS1512+ is scalable via two 5-bay DX510 expansion boxes for up to 15 drives and 60TB.

Link: Synology