Afaik Pu'u O'o ist the only one with flowing lava.
But it is absolutely fascinating to walk on solidified lava flows which can be found in many places in the Halemaumau area! You will never forget the cracking sound if you walk across. almost 7 years ago
Take route 137 west until it dead ends. If you dare, continue walking beyond the chain and signs that say "DO NOT ENTER". There will be other people there as well. You can walk on the solidified lava and see the steam from the flows into the ocean. I think some people also go there at night. The very best views are from off shore. We took a cruise that puttered by. Perhaps there are smaller tours and boats that do something similar. over 6 years ago