The Panama Canal - The entire time we were in Panama, I kept thinking "A man, a plan, a canal, Panama", which if you don't know is the same forwards and backwards. Yes, amazing. Anyways, this canal is also pretty amazing and worth a visit. Come in the morning or at 2pm when the ships are passing through. The Miraflores Locks are the closest to the city, and a $15 cab ride will get you there. If you can figure out a bus, you can probably get there for <$1 but we never mastered the bus system.
The Amador Causeway - A peninsula that stretches into the Pacific ocean lined with palm trees and offering a great view of the city. It's not far from Casco Viejo. There's also a ferry that leaves here for an island 12km from the city that has the closest beaches available. Call ahead, tickets were sold out when we tried to go.
Casco Viejo - The old city is still quite dilapidated, but still worth a wander around. There's a great museum about the Panama Canal and Panama's history called Panama Interoceanic Canal Museum as well as a cheap and tasty lunch spot called Rene Cafe. There are also many night attractions - jazz, restaurants, but we didn't get out there. It's also currently being restored and it's rumored it might one day look very nice.
It's Just Like America, but they Speak Spanish - As far as transitions go, it's pretty easy to keep using dollars, be able to find a lot of the same food in the store, be able to watch the same movies and listen to the same music.
Hostel Panama by Luis - My review on hostelworld says it all: “Location, location, location - this one is not in a good one. We had to take cabs every time we wanted to go anywhere. Cleanliness was another big problem - the kitchen was a mess, the fridge hadn't been cleared in a while, there were cockroaches on the patio, and the room was a bit drab. Finally, where was the staff? Luis was gone for two whole days leaving the front desk unattended. Guests checking in were left on their own to wait all day, and guests checking out couldn't get their deposits."
Taxis - This was largely our biggest source of expenditures, because on depending how badly we were being ripped off we could expect to pay $2.5 (actual) to $15 per ride (only once when we didn't know better). My advice is to ask locals what the actual rate is - or figure out the buses which only cost $0.25.
Lack of Beach - It's crazy to me that you can be surrounded by ocean yet there is no beach in sight. In fact, aside from the island above, the closest good beaches are 2hrs away.
Pollution/Dirt - Regulation of car exhaust must not yet have come into social conscience because buses and cars constantly drive by belching black fumes. The air is gross.