I visited a conference on the big Island last year. I did not expect to be able to play tourist much, but I was able to sneak out for a day and go to see the volcanoes. I saw the lava stream into the sea, and also lots of awe-inspiring geology.
Here is a panorama of the Halema'uma'u crater, which is down inside the Kilauea caldera. Native Hawaiians say that Pele lives inside and the lava lake apparently periodically melts (larger size on flickr).
These are thermal vents on the edge of Kilauea's caldera. Sulfur and other minerals get carried up and deposited by the steam. Very smelly but gorgeous colors.
Colored lava. This is down in Kilauea caldera: