I use a Tom Aquatics Surface Skimmer and it works great. Costs like $13-15 I think. You may have to do a little bit of DIY to get the tube to connect to your canister tube if you have one (I didn't have to though). You use it as the intake to your filter.
Like the poster above, try more surface agitation first, if the surface scum is there around, get a surface skimmer.
I too have a fluval surface skimmer in my tank, it is one of the best buys for my open top tank. My water surface is crystal clear, it does add more bulk to the tank, but it is worth it since increases water agitation didn't work for me.
One of the old tricks to actually remove surface scum, rather than just break it up, is to lay a paper towel on top of the water and then immediately remove it. The scum gets picked up by the paper towel.