Two pieces of Grand Theft Auto IV news today. First off, computerandvideogames.com has posted an article on some "hidden extras" featured in Liberty City. We have summed up the article below.

-Flushing Meadows (Parody of the New York's World Fair) is featured. Also, a recreation of theme park, Astroland. Rides seen in trailers, such as the Corpse Ride and Cyclone, can be rode.
-Arcade games such as Go Go Space Monkey, which we have seen in previous IV Screenshots and in San Andreas.
-RS Haul, a trucking company from San Andreas, returns with missions. (RS Haul has been seen in previous IV screens)
-The Videogeddon Arcade, an arcade seen in a previous screenshot sent to fansites, allows you to play arcade games.
-The NRG500, a motorcycle, is confirmed to be in. Also, a new motorcycle, the NHG900RR, is confirmed to be in.
-Liberty City contains various photos of Vice City. (A photo from Love Meet also features a guy with Vice City in the background) References to older GTA games, in the form of graffiti, is also in Liberty City.
-Various companies from older GTA games such as Binco, Burger Shot, 24-7 and Clucking Bell will all be making a return. Brands from previous GTA games are also making a return.
-Classic vehicles such as the Stallion and Comet from previous 3D GTA games are in IV.
-Alderney has several strip malls where you can purchase food, clothing, and more. Much like the mall in Vice City.
-As detailed in previous reviews, mini-games such as basketball, pool, golfing, and darts will be in.
-Several references to "Hot Coffee" (The sex mod for San Andreas) will be scattered around Liberty.
-Gruppe Sechs, a securicar company all the way back from GTAIII, will be making a return.It is said that you can steal them and deliver them to certain locations for a reward.
-Sprunk can be purchased. Just like in San Andreas, Sprunk will refill your health.
-Various phone numbers are scattered around the city and you are able to call them.
-News tickers on buildings around Liberty City will be almost constantly updated with news about crimes you commit.
-It is said that GTAIV has references to Crackdown. As most of you may know, it was made by a company called "Real Time Worlds" which was founded by David Jones, founder of DMA Design, which is now Rockstar North.

Also in Grand Theft Auto IV news, GameKult had posted twelve new multiplayer screenshots but their page has since been broken. However, Gamersyde was able to get the same twelve screenshots but with a small watermark. We'll try to track down the un-watermarked screens. (Thanks to Ciaran for the alternative source)

Source 1: Computer And Videogames
Source 2: Gamersyde