It's not really a wiki (in that it's not really designed to have tonnes of links between pages), but depending on how loose your definition is, Backpack is a nice choice. It lets you create semi-structured pages containing various bits of data (text, pictures, lists, attached files, dividers, linked text documents).
It's a lot nicer to work with than a traditional markup-based wiki, but it's not as powerful. I personally find the idea of a personal wiki way too prone to fiddling, and Backpack is a nice compromise.
They don't advertise it on the marketing site, but there's a single-user $7/mo plan that gives you 100 pages and 1GB of storage (you'll have to register then change plans), which is more than enough for a personal wiki.