Software Update rocks, but I didn't know about a cool feature of it until, yet again, my uncle recently pointed it out to me. You may notice that if you don't select some packages to update on your system, they'll continue to show up in subsequent package lists when you go to update again. The trick is to select (but not check) the packages you don't want to see and use "Make Inactive" from the Software Update "Update" menu. Using this, I was able to ignore such delights as Traditional Chinese Language Support and friends, preemptively saving myself some space in the process.

If, in the future, you want to see those inactive updates again, you can easily select "Show Inactive Updates" from the same menu.