There are a number of different options for this IcP. Pick the one that fits in with what you are planning to do for your project. If none fits, do the multithreaded sorts.
URL Reading - For this option you will be doing multithreading to pull down a collection of web pages in parallel.
Map Editing - If you are doing a game that includes any type of map or background that has the be built by the user, then this option is for you. You will be writing code that allows you to edit your map directly instead of editing a text file to do so. You can choose how you want to save the map once it is edited. You can use XML or a binary format. If you are doing a MUD, this is a text based editor, otherwise it is a GUI.
Worksheet Saving - This is for the Mathematica option. You should start working on ideas for what your "worksheets" will have in them. These sould probably be represented with some type of inheritance hierarchy that can include formulas, general text, plots, whatever. Consider putting together a little GUI that will let you edit one or two parts of this. The main thing is that you should be able to save off and load back in a worksheet using Serialization.
Multithreaded Sorting - Work on making a polymorphic sort that is multithreaded. You can pick the sort you want to use. Realize that some sorts multithread better than others. Do some timing with different numbers of threads on larger collections. Different machines have different numbers of cores. Look at /proc/cpuinfo to get this information on the Linux boxes.
Paint - For a later semester.
Multithreaded Simulation - For a later semester.