Knapsack lets you build your itinerary (with the requisite pushpin world map), create checklists and postcards for each destination, and plan your daily activities for each trip. Once your itinerary is locked, you can send it out to family or colleagues so they can track you down if needed. Knapsack's got a clean, Bento-ish UI that soothes the travel-anxious brain (see the screencast for a sample).
For $39.95, it's a bit of a unitasker -- if you're already using a notebook, organizer or task-management app, it may be easier to leave your itineraries with the rest of your stuff. One might have expected Knapsack to implement iCal sync or integrated search with Orbitz, Expedia, etc., but I imagine that there are plenty of future features in the works.