1.Algeria - Les Fennecs (The Desert Foxes)
Algeria is over 80% desert. The Fennec (Arabic for fox) is a small nocturnal fox found in northern Africa.
2.Argentina - La Albicelestes (The White & Sky Blue)
The colors of the stripes on their jerseys, and on the Argentina flag.
3.Australia - Socceroos
Soccer + Kangaroos = Socceroos. rofl
4.Brazil - Seleção, Canarinhos, Verde e Amarelo .
The Selection is self-explanatory. The jerseys are canary yellow with green trim. Samba Kings is a reference to both Brazil's style of play, and a Brazilian style of dance. Apparently they are the kings at both.
5.Cameroon - Les Lions Indomptables
Plenty of lions in Cameroon, not many of whom are particularly submissive.
6.Chile - La Roja, El Equipo de Todos

Red is the color of the Chile jersey, and they're Everybody's Team because most neutrals enjoy their attacking style.

7.Côte d'Ivoire - Les Elephants

The Ivory Coast was once home to thousands of elephants, and a roaring ivory trade. Now there are only a few hundred elephants left. Because of the previously roaring ivory trade.

8.Denmark - Danish Dynamite, Olsen-Banden, Olsen's Elleve

The brilliant Denmark team of the 1980s was called Danish Dynamite, while the current are nicknamed after coach Morten Olsen. Sounds like a short term strategy for a nickname, but Olsen has been in charge since the year 2000. Plus Olsen's Eleven is a world class pun.

9.England - The Three Lions

There are three lions on the Football Association crest, in reference to the total number of lions ever spotted in England. Or because of the English coat of arms.

10.France - Les Bleus

France's jerseys are blue.

11.Germany - Nationalmannschaft

Because it's true.
12.Ghana - The Black Stars

There's a massive black star in the middle of the Ghanaian flag.

13.Greece - Galanoleyki, To Piratiko

Blue and white are the colors of the jersey and the flag. The Pirate Ship was a nickname earned at Euro 2004, when Greek commentator Georgios Helakis referenced a boat in host nation Portugal's opening ceremony and said Greece should "become pirates and steal the victory". Which they did.

14.Honduras - Los Catrachos

Because that's how other Central Americans refer to Hondurans, in honor of General Xatruch.

15.Italy - Azzurri

Because Italy's jerseys are blue.

16.Japan - Blue Samurai

Jerseys are blue, and Samurai were "the military nobility in pre-Industrial Japan." Also, Samurai sounds badass. eek

17.Mexico - El Tri

Three colors of the Mexican flag are green, white and red.

18.Netherlands - The Oranje,La Naranja Mecanica

Orange is the national color of the Netherlands and the color of their jerseys, all of which can be traced back to the House of Orange-Nassau royal family. Clockwork Orange is - I believe - half a reference to Anthony Burgess' novel, half a reference to Total Football.

19.North Korea - The Chollima

The Chollima, or "thousand mile horse", is part of Korean mythology.

20.New Zealand - The All Whites

Racism. No, not really. The famous New Zealand rugby union team go Johnny Cash and wear black head to toe, and so are known as The All Blacks. To differentiate themselves the soccer team has wears all white.

21.Nigeria - The Super Eagles

The Nigerian Football Federation crest features an eagle perched atop a football. A super eagle.

22.Paraguay - La Albirroja, Guaraní.

The jerseys are white and red, while the Guaraní are a people indigenous to Paraguay.

23.Portugal - Selecção das Quinas

Refers to the five shields on both the Portuguese Football Federation crest and Portuguese flag, representing the five kings conquered by King Alfonso I.

24.Serbia - Beli Orlovi

The Serbian coat of arms features a double headed (mutant?) white eagle.LOL

25.Slovakia: Repre

A lack of imagination? Repre is short for reprezentacny tim (representative team).

26.Slovenia: Zmajceki

The coat of arms of capital city Ljubljana features a giant dragon sitting atop a castle.

27.South Africa - Bafana Bafana

A term of endearment. Even after the 3-0 defeat to Uruguay.

28.South Korea - The Taeguk Warriors

Taeguk is a Korean symbol of balance. The yin and the yang. You can see it in the center of the Korean flag.

29.Spain - La Furia Roja

Red jerseys. Furious red jerseys.

30.Switzerland - The Schweizer Nati

Because nicknames are hard to come by if you spend all your time being neutral.

31.Uruguay - La Celeste

Sky blue jerseys.

32.USA - The Yanks

Shortening of Yankees, a colloquial term for Americans.