The Nexus line is due for an update, with each product being released for at least a year. They are devices which embody Google's vision… for their own platform. You can fall on either side of that debate, whether it guides OEM partners or if it is simply a shard the fragmentation issue, if you even believe that fragmentation is bad, but they are easy to recommend and a good benchmark for Android.
We are expecting a few new entries in the coming months, one of which being the Nexus 9. Of note, it is expected to mark the return of HTC to the Nexus brand. They were the launch partner with the Nexus One and then promptly exited stage left as LG, Samsung, and ASUS performed the main acts.
We found this out because NVIDIA spilled the beans on their lawsuit filing against Qualcomm and Samsung. Apparently, "the HTC Nexus 9, expected in the third quarter of 2014, is also expected to use the Tegra K1". It has since been revised to remove the reference. While the K1 has a significant GPU to back it up, it will likely be driving a very high resolution display. The Nexus 6 is expected to launch at around the same time, along with Android 5.0 itself, and the 5.2-inch phone is rumored to have a 1440p display. It seems unlikely that a larger, tablet display will be lower resolution than the phone it launches alongside — and there's not much room above it.
The Google Nexus 9 is expected for "Q3".