1. Sheikh Zayed Mosque
This was my favorite sight of Abu Dhabi and a MUST see! The mosque is magnificent, the largest in the country, and free entry! You just have to dress modest, they will inspect you and give you a free abaya to borrow upon entry.
TIP: Go at golden hour (sunset), everything looks more magical at golden hour.
2. Ferrari World
A car lover's dream, Ferrari World. We didn't go inside because a ticket cost $80, no thanks. Ferrari World is not only cars, it is a theme park with rides, shows, and shopping. Instead of paying, just visit the outside of the building and watch exotic cars zoom by on a race track. That was enough for me!
Ferrari World also has the world's fasted roller coaster.
3. Yas Island
Ferrari World is on Yas Island along with Yas Waterworld, Warner Bro's World, a marina, mall, restaurants, hotels, and beach. We visited the beach on Yas Island and it's nothing special. We chose the private beach over the public beach access because the private beach had a pool, cabanas, and towels. It is $10 during the week days for private beach access BUT we didn't realize it was the weekend until we already paid. $30 each with no refunds. :(
4. Corniche Beach
This is the nicest beach in Abu Dhabi with places to eat and shop. There are many rules on this beach, though. Like no touching each other, no music, no photography (phone cameras are okay). They even put ropes in the water restricting how far you can swim. Lifeguards WILL enforce these rules, we heard their whistle ever 5 minutes at clueless tourists.
Aside from these few things, I felt like Abu Dhabi didn't have a lot that interested me. Dubai is only 1.5 hours away and has much more things to do but I would still stay in Abu Dhabi for a day or 2.