It seems like everyday a new API is release that's just brimming with exciting possibilities for web app builders. I have a ton bookmarked in del.icio.us and have decided I need to focus my efforts so I can actually get deep into some of the best. What are your top 5? Here are mine:
1. Amazon Web Services
2. Google Charts
3. Google Maps (yes, I'm behind the times)
4. FriendFeed (coming in next few weeks)
5. LinkedIn (release it already, dammit!)