Beets, turnips, rutabagas, parsnips, and celeriac are all starchy staples in my diet, along with sweet potatoes, carrots, and squash.
Taro and cassava/yuca are quite starchy and available at most ethnic markets. If you try out cassava, keep in mind it has to be prepared properly to avoid cyanide poisoning (fun!). It's very tasty, though, as is taro. Green plantains are also very starchy and delicious.
Please let me know if you'd like suggestions on cooking or pairing any of these foods. A great resource that is not paleo but easily adapted is Chez Panisse Vegetables by Alice Waters.