It looks like some pics have finally leaked of the upcoming R520 product along with specs on possible card line ups. 
R520 Spy Pics? - Graphics Cards  1 R520 Spy Pics? - Graphics Cards  2
The card you are seeing is the R520 XT. It is a dual slot solution and uses a cooler similar to the X850. ATI will also offer one-slot versions which will have less performance.

The will only be PCI-Express boards. AGP versions are definitely not planned.
Internally the chip will use 512-bit memory transfers. However, the external memory interface will still be 256-bit – expect some nice marketing from ATI regarding that “feature”.

Right now the product lineup is:
R520 XT
  • 512MB RAM
  • ~600 MHz core
  • ~650-700 MHz memory
  • Dual slot cooling
  • Dual DVI
R520 XL
  • 256MB RAM
  • ~500 MHz core
  • ~500 MHz memory
  • Single slot cooling
  • VGA + DVI
R520 LE
  • 256MB RAM
  • ~450 MHz core
  • ~450 MHz memory
  • Single slot cooling
  • VGA + DVI
R520 XT Crossfire Edition
  • 256MB RAM
  • ~600 MHz core
  • ~650-700 MHz memory
  • Dual slot cooling
  • VGA + DVI