Since there is now road connection between Panama and Columbia, you may consider going by boat.
A realy cool alternativ is the 40 meter two mast schooner Stahlratte.
The ship is usualy sailing between the amazing islands of San Blas/Panama and Cartagena/Colombia.
Starting Oktober 2008 they are planing a longer trip from Panama up the Central American coast to Cuba and Jamaika and back to Colombia.
Check it out on
www.stahlratte.org: Logbuch