Sand is awesome, i have it in my 55 and one of my tens and the fish absolutely love that stuff! plus it looks pretty, cheaper than gravel too if you buy play sand from wal-mart, hah it is a pain to lug around if you have girly muscles like me though
I know this isn't about the topic, but cool user pic managuense! lmao
And on the topic, I use coral sand in my tanks. Its acts like gravel (larger pieces) but has the cool sand look (but not exactly like play sand cause of the larger bits) Its may not be good for yours though since you are doing an amazon tank and might need relatively soft water (the coral raises your ph).
Cichlid-Man raises a good point. Do you plan to use live plants? If so, then gravel laced with laterite is the way to go. The problem with sand from HD or Lowe's is that the sand doesn't have the necessary nutrients for plants to grow. However, there is Onyx sand that contains the necessary nutrients. You can get it at your LFS.