I lived on the Carribean Coast of Colombia for two years. I have heard Spanish from all different countries and to me Colombian Spanish is the most clear and easy to understand. Many other people have said the same thing. Of course, the costeno's or people on the coast speak differently and it is much harder to understand them. The people from the interior of the country like Bogota and Cali speak clearly. If you are trying to learn Spanish, Colombians are great to practice with. You can also check out spanish learning courses from a place like www.spanishsimple.com.
Colombians are great people, despite what you may think with the countries drug and guerilla problems-It isn't as bad as the media says. They are willing to help a Gringo learn their mother tongue, just be ready to handle some joking around at your expense. They love to poke fun at the North American accent. I love Colombia.
Todo "Chevere"
Chris