I'm struggling trying to answer this in a way that would enhance what you've got already. Because really, you've got a pretty good representation of "everyman's speaker" there with the Creative set you have already.
So I'm going to take a different approach here and, instead of recommending something to buy, I'm going to recommend some techniques I use to test my mix to see if it'll work on other systems (I mix on a KRK Rokit setup and my big mains are JBLs driven by a McIntosh amp).
Test on a clock radio. They are almost the ubiquitous music listening device. We all have them in our rooms. There are a few, guaranteed, in every office space. Your mechanic has one in his office. They are everywhere. And they sound pretty much like poo. I have a line in on my little Sony clock radio. I'll bounce a mix, drop it on my iPhone, and try it out on the clock radio via the line in.
Test you mix without the sub. Most people don't have one. So click off the sub on your Creative setup and see how it sounds. Is there still a reasonable representation of the low end happening when it's just a small speaker setup?
Test your mix in mono. Or rather: move away away from the sweet spot. I like to throw a mix on in a loop and then walk out of the room. Wander around the house. Listen to it like most people listen to music: while they're going about they're day and it's background to their lives. Few people spend the time to sit down in the proper spot, between two nice speakers, and really enjoy all that hard work you spent placing each instrument in to it's own space. Sad, but true.
Test your mix in the car. Music and cars are just kind of like pie and ice cream. It needs to sound good in the car.
Test your mix in headphones. If only to avoid the "Sgt. Pepper's Effect" where you've panned things to extremes and when you listen to them in headphones it becomes a bit like having your head pulled apart by the ears. I test headphones last because I find if I tune for them I'll end up with a mix that's too bass heavy on regular speakers.