Ever since I first got interested in electronic music, I have always wanted a modular synthesizer. Though still a bit pricey, they are extremely flexible, fun, very educational, and inspiring to work/play with. I've played with/programmed many, and even borrowed some at various times.
I would still like one. Perhaps a small system like this from BugBrand.
The good news is: they are probably more affordable, well sized, and powerful than ever. This great Sound on Sound guide to buying modular synths inspired me yet again to scratch a long-running itch. In time, I will have one for sure.