Peaberry

Agree with Spirit Island. I also really enjoy the solo mode for Pax Pamir 2e, which is possibly my favorite "bot" opponent. Hallertau is beat your own score solo which works particularly well. I've heard some criticism about the randomness of the cards in that game, but that's not much of an issue playing by yourself.

I'll second cascadia and the button shy games sprawlopolis and ROVE. I've also been enjoying the solo hidden movement game black sonata of late, and it's a wonderful world as a engine/tableau builder