Updated - Synology's DS1517+ is an attractive choice for a 10GbE capable NAS.
QNAP's TS-431X is an inexpensive way to move up to a 10 GbE NAS.
QNAP's TS-231P is a good value in a RAID 1 NAS.
QNAP's TS-228 is inexpensive, but makes performance compromises to get there.
QNAP's TS-431P is an entry-level RAID 5 NAS that should satisfy cost-focused buyers.
Synology's DS416 and DS416j are both good values in four-bay RAID 5 NASes.
TerraMaster's F2-220 Cloud Storage NAS has a good feature set, but isn't a good value in a two-bay RAID 1 NAS.
Updated - NETGEAR's ReadyNAS RN626X has two built-in 10GbE ports and can make good use of them.
QNAP's TS-251A and TS-451A provide the option of direct attached storage with a twist.