In a post on their news blog, Valve announced the title as Counter-Strike: Global Offensive. It will be available in early 2012 for XBLA, PSN and Steam. with the intent to "Expand upon the team-based action gameplay that it pioneered when it was launched exactly 12 years ago (CS beta 1, August 1999)".
The game will feature new maps, characters and weapons, as well as updates to the classic maps from CS and CSS (such as de_dust). There will also be new gameplay modes, matchmaking and leaderboards.
The game will be playable at PAX East and at the Eurogamer Expo in London.
This sounds like a great idea, I personally used to play loads of 1.6 back in the day. It's really exciting to hear that Valve are finally getting around to making a sequel to what was the most played game on steam before Team Fortress 2 became free to play. I'm excited for this to come out, but also can't wait to get my hands on it at Eurogamer this year.