England (UEFA Group 6 winner)
Population: 50 million
Capital: London
Team nickname: Three Lions is probably as close as they get to a nickname.
Best World Cup finish: 1st place (1966)
Coach: Fabio Capello (ITA)
Guys to watch: Wayne Rooney, Frank Lampard (both pictured above), John Terry
Why cheer for them: Many of us grew up watching and loving the English game.  
Why boo them: They're Poms!

USA (CONCACAF winner)
Population: 305 million
Capital: Washington D.C.
Team nickname: Usually listed as The Yanks but I've never heard anyone use it.
Best World Cup finish: 3rd place (1930)
Coach: Bob Bradley (USA)
Guys to watch: Landon Donovan, Tim Howard, Jozy Altidore
Why cheer for them: For one of the few times in the history of sport, the US is actually a plucky underdog.
Why boo them: Let me count the ways: the endless Health Care debate, Jersey Shore, LAX, Fox News, the Kardashian family, __________ (fill in the blank).

Algeria (CAF Group C winner)
Population: 34 million
Capital: Algiers
Team nickname: Les Fennecs  ("Desert Foxes")
Best World Cup finish: First round (1982 and 1986)
Coach: Rabah Saadane (ALG)
Guys to watch: Yazid Mansouri, Faouzi Chaouchi, Karim Ziani
Why cheer for them: They're the least-fancied of any African team.
Why boo them: Perhaps you have a soft spot for Egypt.

Slovenia (beat Russia in playoff)
Population: 2 million
Capital: Ljubljana
Team nickname: Zmajceki ("Dragons")
Best World Cup finish: First round (2002)
Coach: Matjak Kek (SVN)
Guys to watch: Milivoje Novakovic, Robert Koren, Samir Handanovic
Why cheer for them: They're the smallest nation in the entire tournament, with less than half the population of Sydney.
Why boo them: Petulance: the last time they made the World Cup, a player/coach feud disrupted their tournament.