Sweet potatoes, yams, brocholli, asparagus, pumpkin, squash. Just make sure to wash them really well. I do not blanch anything, the plecos seem more than happy to take their pieces without it being soffened up.
I would peel brocholli, sweet potatoes and yams, cut asparagus in half, pumpkin and squash leave the skin as it will help to hold it together and sometimes the like to eat it. Zucchini the same way. You might try microwaving the yams and sweet potato just until they can be scrathec easier with a fork but not too soft. Of course, remove all seeds for anything and don't feed the crowns of asparagus just the stems well peeled. The little flower pods make a mess.