Visas depend a lot on your nationality. In Latin America, for example, an American should expect visa issues entering a country like Venezuela. Fly into Santiago, Chile and expect to pay USD $140 "reciprocity entry fee" into the country (U.S. citizens only.) Expect to pay something similar going into Brazil but with 30 days processing time to get your visa unless you pay more to get it expedited. I think these are the 3 countries that could pose issues, but in general traveling through Latin America on a bicycle is fairly straight forward.
Having said the above, I understand Chile is an amazing country for bicycle touring - check out the Carretera Austral!
Last edited by Chris Pringle; 04-18-12 at 11:45 PM.