Here is a short guide to the countries bidding.
England - Last held cup in 1966. Last Major tournament in 1996. Olympics in 2012. Favourite. Backed by some influential people in UEFA, such as Franz Beckenbauer.
Australia - Sepp Blatter has suggested that Australia focus on 2022. Held Olympics in 2000. Held a 2003 Rugby World Cup, 2006 Commonwealth Games and a number of OFC and Under 21 football tournaments.
USA - Very recently held the tournament, in 1994. Vice president of FIFA (President of CONCACAF) has said he would prefer USA to go for 2022. Very large number of stadia (58 confirming interest).
Spain/Portugal - FIFA would prefer not to give the tournament to a joint bid. Spain held the tournament in 1982, and Portugal held Euro 2004. Large number of eligible stadia, including 8 UEFA 5-star rated stadia.
Indonesia - Focused on holding the Cup in 2022. 2018 is more of a back-up bid. Low standard of national squad. Relatively poor infrastructure.
Japan - Joint held the World Cup only 7 years ago (16 at time of tournament). Banking on Tokyo's bid for the 2016 Olympics, for the building of a new stadium.
Mexico - Held the World Cup twice already (albeit once and a late replacement). Working on 13 new stadiums, and already has the world's fifth largest stadium. Very high temperatures in summer could work against the bid.
Russia - 5 stadia fit to host the World Cup will be ready for 2013. Hosting the Winter Olympics in 2014. Expected to work against the bid is the sheer size of the country. Situated in 9 time-zones, the scheduling would be a nightmare for FIFA.
Netherlands/Belgium - Recently held Euro 2000. Like the Spain/Portugal bid, Blatter suggested that joint bids would be rejected if a suitable individual bid was available. There is no stadium over 80,000 to hold the final.