Try the 'Video Outfit Kit' at AP. It contains a Lead-acid battery and a lamp assembly which includes a 100W quartz-halogen bulb. Costs around $100. The lamp fits onto any standard hotshoe, and is lighter than a full-sized flashgun.
I use it when doing videography, and it is heavy, but not overly so. If 100W is too powerful, there are bulbs of 50W and 35W. Costs around $5 at SL Tower. Battery run times are approx 45min when used with the 100W bulb, and 90min for 50W bulb. Light output is tungsten-like, but if used with flash, just a slight correction for WB should do the trick.
There are also replacement lead-acid batteries of smaller capacities and shorter run times, but are a whole lot lighter and more portable. Also can be purchased from SLT.