Daylight LED lamps. Many of these are daylight rated that is 5500-6000K. I have just purchased two portable 23W/1400Lumen ones from Screwfix. Taking the base off and mounting them on flash stands (need to buy bits and pieces from Amazon) has given me a cheap way of adding support lighting to my 580EX II flash which I also mount on a stand with a diffuser and remotely trigger using hahnel Tuff TTL triggers.
Although not as effective or powerful as professional LED lights they are much cheaper at £30 each. They recently solved a problem at a wedding which was in a barn. They allowed me to take wider shots by mounting a light source either side of the small groups. Being portable they let me move them around quickly and not have trailing cables. I also have a 30W mains powered unit and find them all a lot more convenient at this type of even than my studio flashes.