JNUG, NUGT, JDST, DUST are the most volatile among leveraged ETFS.
There are many good, leveraged ETFs based on indices: TNA, TQQQ, SPXL, etc.
TQQQ, 09/2010 4.76, today, 88.39 (nasdaq 100)
SPXL, 03/2009, 4.84, today 126.05 (SP 500)
TNA, 03/2009, 5.70, today 101.93 (RUT 2000)