From the looks of your tank age based on your profile I would caution against adding any type of Nem for at least 6 months. (I am assuming you are talking about for your 40 Gallon.) Even the slightest change in anything can upset them. I understand it's not a big deal as it's only $7/8 if you get a cheapy nem from Petco or someplace like that, however every nem that dies in the home is one more nem that should have been left in the wild to serve as protection for some pair of clownfish.
Before you decide to purchase a Nem please be sure your lighting is up to par. Anything under about 4-5 WPG is a huge disservice to your nem and will probably stunt its growth or kill it slowly over time.
Lastly, clowns don't need to host an anemone to live. They can live and spawn perfectly normal if you offer some type of suitable replacement. I have heard many people say they like the clay flowerpots. I have also seen pictures of somebody's pair spawning inside the clay flowerpot. Good luck with your new tank.
