For my fellow Anglos who need their peanut butter and "real" cheese sometimes:

Carulla — the most "international" grocery; reliable for most imported brands
Pomona — premium and slightly cheaper than expat-Carulla
Olímpica/Surtimax — Colombian-mainstream but they have a foreign-food aisle that grows every year
Makro — Costco-like, bulk; surprisingly good for imports
Justo & Bueno — discount; don't go for imports, but go for everything else