Bogota: The weather isn't always so great here - I was only there for 2 nights, and it was raining quite a bit during that time. The nightlife is rather good though and makes up for the often inconvenient weather, you can usually find a party any night of the week!
Cali - the Salsa capital of the world! I observed some of the best dance moves I have ever seen in my life here.
Salento – I joined one of the famous coffee tours, Finca Don Eduardo, and it was worth paying a bit more than the other tours for. The (Australian) owner gave the first hour of the tour in English, describing the full process of how coffee is produced. Following that, one of his workers, Julio, explained (in Spanish) and demonstrated parts of the process, and then we actually went out into the fields to see where and how the coffee cherries are handpicked. This was an eye-opening experience, and one of my favorites on the trip! I will never look at another cup of coffee with such simplicity again. From Salento, you can also do a hike through Valle de la Cocora, which has amazing wax palms and a hummingbird sanctuary.
Pereira - I stopped in this city on my way up to Medellin to experience a less touristic Colombian city. It was nice, though I have nothing special to report about it.
Medellin - The days of Escobar are long gone and some of the seedier parts of the city have been transformed into uplifting projects and governmental departments. Riding in the cable cars to get a glimpse of the city and its recent accomplishments is a great idea. Taking the free walking tour in Medellin is an ever better idea - you will gain an unbiased view of the city and how it has transformed over the years!
Cartagena - The old city is beautiful, majestic, and certainly worth at least a day or two of exploration!