I know the Synology range of NAS's are compatible with the new 3TB drives, namely the Western Digital WD30EZRS-11J99B0 ($200) and Seagate ST33000651AS (no prices)
Prices are from NewEgg and do not include hard drives
Models to choose from Synology
DS411j - 1.2GHZ CPU 128MB RAM - $350
DS410 - 1.06GHz CPU 512MB RAM - $500 (may soon to be replaced with the DS411, which I expect to have a 1.6GHz CPU and 512MB RAM)
DS411+ - 1.67 GHz dual core CPU 1GB RAM - $630
DS1511+ - 1.8GHz dual core 1GB RAM - $870 - this is actually a 5 bay model which can be expanded with up to 2 x Synology's DX510 expansion units, giving a possible 15 total drives
I was going to list QNAP's 4 bay models, but after looking at their web site, they don't appear to support the new 3TB drives yet