I'm still happy with my ReadyNAS NV+ that I used to replace my Linux server. I was in a similar situation where I realized it was silly how much equipment I had on all the time and was maintaining. While the server used to be a mail server and small web server for my friends back when I had a dedicated connection for it, ever since my move it was just a glorified SMB/AFP box.

Anyhow, the reason I picked the ReadyNAS was because it met my core requirements for a NAS, and they were:
1. Support AFP. With my heavy OS X usage, AFP is handy to have as it tends to work better then SMB.
2. Stream media via iTunes and uPnP protocols.
3. Be expandable in a non destructive way. I'm currently running mine with 3 750GB drives in "X-RAID" mode. X-RAID is just a marketing name for a system to pick the best RAID level for maximum usable space based on the drives in the system, tune the RAID For media performance, and also allow expansion. IE, you could start with one drive, and set it as X-RAID. No redundancy, but the system would support adding a second disk to then gain RAID-1 with no downtime. Add a 3rd, and the RAID transitions to RAID 5, and adding a 4th expands to all 4 disks with RAID 5.

Management is all web based, and has some nice features like allowing packaged addons to be added quickly. Under the hood, it is running Linux, and they do allow users to SSH in and work at that level if desired. Processor wise it runs a little SPARC chip, then uses a hardware RAID chip to avoid the RAID calculations from tying up the CPU. While the hardware RAID chip did concern me a little with portability, the 5 year warranty helps alleviate my fears of being away from the data too long if the hardware fails.

Their support community is also really good, and has not degraded even after Netgear bought the company. Their boards are here, and their developers regularly participate and answer questions.

Some useful features include UPS integration for powering down during an outage, the ability to share USB printers, or USB disks over the network, the ability to schedule the device to turn on and off at different times during the week, and a decent monitoring system that can e-mail you any issues that arise.