It looks like Asus may have a new Android tablet in the works, on top of the new Asus Transformer Prime, and this new device comes with the model number of TF300T.
Asus recently announced a new Transformer Prime with a higher resolution display, and that came with the model number TF700T, so this new TF300T could possibly be a budget version.
Unfortunately all we have at the moment is these pictures, there are no details as yet on exactly what the device might be, although it could possibly be a budget version of the Transformer Prime with the higher resolution display, but a dual core processor instead of a quad core version.
Updated 3rd June 2012
The Asus Transformer Pad TF300 comes with a quad core NVIDIA Tegra 3 processor, you can find out full details here.