For me, side projects are about cash, not fun. I try to find contract jobs that look easy, bid really high knowing I won't get the vast majority of them, and do a good job for the people who actually hire me.
[I write C, C++, do algorithm development, and also automation -- anything from embedded firmware to large optimized math for HPC, to even the (non-UI side of) mobile apps. I've done some amount of contract work in the past but am in the middle of a long (and annoying) dry spell and looking for new sources.]