Here is a rather extensive collection of 350+ data structure problems with solutions. The list varies from the usual searching and sorting of values in an array, to string manipulation, binary logic, matrices and graphs. No matter how high was your grade for all those Computer Science courses back in college, or how long have you been programming, I guarantee you’ll find a challenge or two in this list.
From a very brief couple of hours look at the list, my favorite ones seem to be around the chessboard problems, such as this chess knight problem for finding the shortest path to destination using a queue.