Since you only got a 40 Gallon, You could go with this one!
Amazon.com: Reef Octopus Hang-On- Back Protien Skimmer - BH100: Pet Supplies
It's smaller so it wouldn't be too much of an eyesore like mine is. It's rated up to 60 gallons. If I had to to it all over again, I would have got this one. I have the BH-1000 on a 29 gallon, and it's huge!! The only good thing is I am going to use it for the new 55 gallon I am upgrading too by the end of next month.
Also about the Canister filter. I have had mine on for longer than 3 months now. As long as you are good with the cleaning, you should be fine. It really helps keep my water clear. You got to clean it every week! It does not take me long to clean...