The Half-Life 2 Zero Point Energy Field Manipulator Replica will go on sale in April, but they're going to be pretty tough to get hold of. Joystiq have noticed a sales page on Think Geek offering NECA's 1:1 model for $150. There will only be 5000 sold worldwide. Once they sell out, "they're gone forever!" The two foot gun features "orange LEDs, 2 handles, 2 triggers, 4 unique sounds from the game." You'll find a list of pre-order links here on the NECA pre-order page .
I think I prefer their Portal gun , but sadly that's flown out of stock. All that's left is a little note saying that the entire batch went in less than half an hour. There's more merch on the NECA site , and you can get a closer look at the Gravity Gun replica in this photograph right here.