Tom Clancy's Splinter Cell: Chaos Theory was the first game in the Splinter Cell series to feature a knife as a part of Sam Fisher's arsenal.
The game features fairly prominent product placement during cutscenes, in loading screens and on the screensavers of in-game computers. For instance, there's a gratuitous closeup of a Wrigley's Airwaves pack of chewing gum in one cutscene; the Airwaves logo later shows up on a zeppelin seen in the background.
Amusingly, the advertising features both popular brands of PC CPUs; the main sponsor in Europe is the AMD 64 brand, whereas Intel logos adorn the North American version.
The game makes numerous references to Metal Gear Solid 2, the most obvious one being in a particular knife-to-throat interrogation:
"It's not like you can shake me and make my ammo fall on the floor to pick up"
-- which is of course something you can actually do in MGS2.