I've started Zulu War stuff in 1/72, mainly driven by the lovely models available for both British infantry and Zulus, but with the huge array of stuff available from HaT now (cavalry, artillery, Gatling guns, mounted infantry, European paramilitary units, Natal Native Contingent, wagons galore) it's a killer.
Napoleonics are a must, and Airfix's 'La Haye Sainte' set is utterly to blame. I'm even planning an article about building an accurate Highlander regiment purely using Airfix models, but with conversions to add things like the water bottles and satchels.
WW2 Desert War goodies, with Western Desert Force using 8th Army and plastic vehicles of course.
And last, but possibly least, there's a big wedge of Early Imperial Romans and Britons, ready for one of those projects that I know will never happen - Boudicca.