Careful with Drobo. When they are working, they are great. But just know going in they use a proprietary disk structure, so if you have issues and need an emergency recovery if the array fails you can pretty much forget about it. I was burned once, and I am more careful now.

I have been using ReadyNAS since their Infrant days, they are not too bad.

I am always looking to build a more perfect beast, I am debating giving Synology a go. I hear great things about them...

Another +1 for Synology!

You can also cook your own with a HP Proliant Microserver and throw one of the many free and open source NAS software on it.

Much information at the various pc enthusiast forums like HardForum and Silent PC Review.

They make a bunch of cheap, single hard drive NAS's now. Not bad if you don't care about RAID or support for every type of media server and network protocol.

I'll also say that if you're in the iTunes world, the only solution that truly supports all your iDevices well is a Mac running iTunes 24/7. In my case, I ditched the multi-disk NAS (Infrant ReadyNAS) and just leave my MacPro on all the time.

ALso, if you have an old PC laying around that has seen better days, it can make an excellent server using UNRaid.

It's even free!

I am using a 4-slot Drobo with DroboShare (NAS/ethernet) option. I love it.