My next target will probably be the C3 Big Box, which ZMG has released in the UK but not North America yet.
The only other items I'm missing are the Russian promos, most of the Spiel tiles, and Cutcassonne. I don't expect that I'll be able to get my hands on the first two at a reasonable price, so I might go the homemade route. I also have plans to print some of the C1/C2 conversions from our German friends. Cutcassonne will probably be available again at the end of the year.
The next item to arrive will hopefully be Sokol, which I preordered last month. I've also just ordered some tile bags for H&G.