Here are the pictures found in The Final Hours of Half-Life:Alyx that show off beta content and such.
DownloadAnimation Sheets:
Antlions:
Blind Zombie/Jeff:
City 17 Concept Art:
Characters:
Combine:
Early Basement Level:
Miscellaneous:
Painted over screenshots:
Red Door Ending Concept:
Screenshots:
The Vault Concept Art:
Whiteboard Sketches and such:
Xen Fauna Art:
Zombie Renders: