For lower power stuff I use the MFJ-264. Don't believe the rating you see. that is only for about half a minute or less from a cold start. It will handle 100 watts continuous.
For more demanding situations I use my homebrew load made from ten 500 ohm, 200 watt watt Globar resistors all mounted in a 12 quart stock pot and filled with silicone load oil. I must admit it is pretty sad when your tubes don't have handles but your dummy load does. :headbang This load is good for 2000 watts in air and God knows how much in the load oil. I figure it's good for 10Kw at least. It has had 4 Kw peak into it for 15 minutes straight and was only just beginning to get quite warm near the top.