Here are some of the upcoming slate PCs (tablet notebook hybrids) that I've found, feel free to add more!

Acer:
W510 (10.1") - IPS, SIM card slot, microSD slot, USB2
W700 (11.6") - 1080p, USB3, Thunderbolt, 5MP rear camera
Source

Asus:
Tablet 600 (10.1") - 1366*768 IPS, Tegra 3, 2GB RAM, Windows RT, 8MP rear camera
Tablet 810 (11.6") - 1366*768 IPS, Intel Medfield, 2GB RAM, Wacom dual digitizer
Transformer Book (11.6"/13.3"/14") - Ivybridge, 4GB RAM, 5MP rear camera
Sources: Tablet 600/810, Transformer Book

Compal OEM:
OEM 11.6" - 1366*768, AMD A6 Trinity
Source

Gammatech:
Durabook U12Ci (12.1") - 1280*800, Ivybridge, USB3
Source

Microsoft:
Surface (10.6") - HD, Tegra, Windows RT, USB2
Surface (10.6") - 1080p, Ivybridge, USB3, mini DisplayPort
Source, Hands on

MSI:
Slider S20 (11.6") - 1366*768, Ivybridge, 2x USB3, ethernet (technically not a hybrid as you can't detach keyboard though)
Source

Samsung:
Series 5 Hybrid
Source

Toshiba:
Unnamed
Source

It's interesting to see how these will develop. I firstly thought that they'd actually take away both the tablet and ultrabooks but then I realised:
- Android tablets will exist as they will be cheaper and weigh less, providing more of an entertainment device.
- Ultrabooks will stay as they will be thinner and also weigh less, due to their design.

Although manufacturers have come a long way, you can't escape the fact that tablet notebook hybrids will have most of the hardware in the tablet itself with the keyboard dock not having much more than a battery and some weighs in it to prevent it from being unable to maintain it's balance. If manufacturers were able to turn the keyboard dock into more by adding discrete graphics, more connectivity etc, these could really expand.

Of course, these are still a niche product though but I can see them being successful. I'm definitely going to be picking one of these up!

I wish AMD would up their game though; I'm sure their APUs are more than up to the task of being compatible (TDP, size and performance wise) for being inside a slate PC, but I haven't seen any manufacturers take up an APU for their tablet...