Valve announces plans to show off Left 4 Dead 2 at Comic Con 2009 (albeit the Xbox 360 edition), which gets underway today in San Diego, CA. Here are some new screenshots showing the Swap Fever map and the Spitter infected, and here's the outline of what they're bringing to the show as a preview of the many previews that will follow:

Left 4 Dead 2 (L4D2), the sequel to the best-selling and critically-acclaimed co-operative multiplayer thriller, is being shown this week at Comic Con, San Diego.

The game is available to play, by the press and public, at the EA Gaming Lounge presented by Xbox 360 (from 2-9 pm Thursday-Saturday, and 12-5 pm on Sunday) and the Xbox 360 booth, (booth 5225 Hall G) all day on Saturday July 25th. The EA Gaming Lounge is located in the Hilton San Diego Gaslamp Quarter Hotel, 401 K. Street.

After debuting "The Parish" campaign (set in the New Orleans' French Quarter) at E3, the Comic Con showing unveils "Swamp Fever", the second of the five campaigns shipping with L4D2 this fall.

Valve is also unveiling a new Boss infected monster coming in the full version of Left 4 Dead 2. Known as "The Spitter" this is the second new Boss infected from L4D2 revealed thus far (the Charger was revealed at E3). The female Spitter has an area attack that can split up Survivors or flush them out of their hiding spots. At least one more new Boss infected is expected to be revealed before launch.

In addition to the new campaign and boss monster the Comic Con showing of L4D2 also includes the debut of the "Mudmen," the "uncommon common" exclusive to the Swamp Fever campaign, and a few more of the 20-plus new items coming in the full product (cricket bat, AK47, and grenade launcher).

Coming exclusively to Xbox 360 and PC on November 17, Left 4 Dead 2 promises to set a new benchmark for co-operative action games and become one of 2009's marquee titles.