It will be several months at least before I can go, but what would be an ideal itinerary for 10 days? I was thinking half the time around Medellin and the rest on the Caribbean coast. Any other recommendations? It seems like a long bus ride between the two. Any good places to stop along the way. And finally, Is winter the dry season as it is in Central America?

there are some flights from medellin to capurgana a small resort town at the panamian border, which is quite nice, or the busride of course

agree with bickerss - unless you have the money to take several flights, stay around the carribean. Otherwise the combination of that with medellin is very nice, but in such a short amount of time, you ll have to fly to cartagena and back to bogota, at least.

Just did 10 days in Colombia w/ my gf, too..
*We found having A/C in hotels was required for us to sleep nicely.
*I wasn't impressed with lodging in Taganga...stay in Santa Marta instead. better value. Taganga doesn't have much going on besides diving..so you may not need to stay there.
*Mini-bus transportation between Cartengena andTaganga/Santa Marta should cost $40.000 per person. Count on 5 hours of travel between 2 cities.
Add in a visit to Tayrona National Park and you'll get the whole package.
Days 1-5: Hike Cuidad Perdida (we did it in 4 days.. 5 is fine, too)
Days 6,7: scuba dive in Taganga, visit Bolivar's house in Santa Marta
Days 8,9,10: Cartengena... enjoy the sites.
Santa Marta - Hotel Nueva Granada
Cartengena - Hotel 3 Bandaras