Nomad Lounge is probably your best bet. It's really nice. My second choice would be Dawa Bar in Harambee - those bartenders are fun and I love the music in the area. However, sometimes it's not easy to get a seat. Finally, if you want to bring a beer into the Rivers of Light show, the Thirsty River Bar & Trek Snacks, just to the left of Expedition Everest when looking at it, has some nice selections.