A trip into the
rainforest is an obvious must.
The Meeting of the Waters is quite a sight. Just outside of Manaus, the jet black Rio Negro meets up with the sandy brown Rio Solimoes and, due to a number of factors, including differences in speed and temperature, the two run side by side for several miles before mixing to become the Amazon River.
Even if you're traveling on a budget, try and spend at least one night at the Hotel Tropical: a world-class resort with a mini-zoo, orchid garden, shopping mall, and a wonderful pool area. It's an attraction in and of itself.
Finally, see if you can get to one of the local villages. It will give you a glimpse of how the inhabitants of the region live, and a chance to buy handcrafts.
Quick Tips:
There are a number of ways to experience the rainforest. You can hire a guide to take you on a camping trip, go on an organized tour, or stay at a jungle lodge. Whatever option best suits you, make sure you do some research and ensure that you are going with a reputable company.
The Rio Negro is a pleasant place to stay, and many of the jungle lodges are located there. Many insects, including mosquitoes, cannot live there due to the high acidity of the water, so it's much less "buggy" than the Amazon River itself. (Nonetheless, it's not bug-free, so bring some repellant with you.)
Read Pamela Bloom's book, The Amazon, before you go. Some of the info is a bit outdated (the book came out in 1995), but it's still an excellent resource.
Best Way To Get Around:
Taxis can get you around Manaus.
Many of the jungle tours leave from the pier at the Hotel Tropical.