I'm thinking beyond just those really-high-graphics kind of screenshots...more preferrably the kind of thing that seems extremely epic and could sell the game on its own. To start off with, here's some from the Garry's Mod forums.
http://img100.imageshack.us/img100/4459/shef66701be9.jpg
http://img524.imageshack.us/img524/5498/shef62404uw5.jpg
And the famous Episode 2 shot
http://store.valvesoftware.com/img/productpage/getthegear/Zoom_HL2EP2poster.jpg
And just so I'm no HL2 fanboy, a Metal Gear Solid shot.
http://xtreview.com/wallpaper/albums/New/Metal%20Gear%20Solid/normal_Metal-Gear-Solid-02-1024.jpg
Fit so perfectly with the caption "THIS IS NO FPS. THIS IS MGS."
http://img100.imageshack.us/img100/4459/shef66701be9.jpg
http://img524.imageshack.us/img524/5498/shef62404uw5.jpg
And the famous Episode 2 shot
http://store.valvesoftware.com/img/productpage/getthegear/Zoom_HL2EP2poster.jpg
And just so I'm no HL2 fanboy, a Metal Gear Solid shot.
http://xtreview.com/wallpaper/albums/New/Metal%20Gear%20Solid/normal_Metal-Gear-Solid-02-1024.jpg
Fit so perfectly with the caption "THIS IS NO FPS. THIS IS MGS."