Here’s an interesting and popular tutorial that I have posted in one of my YouTube Playlists. It takes advantage of fluid particles, clumping together and rising slowly like a lava lamp works. The key is to set the gravity to 0.0 and to emit the particles at a very slow rate (less than 1). Here’s the link: http://youtu.be/aLE79LWsvk8
This tutorial is one of over 300 tutorials that I organized into Playlists for new and intermediate Blender users. Enjoy!