Are your seedlings stretching on you? Tomato plants getting too tall before planting time is often a problem, and one I've had in the past. Give them as much light as possible, fertilize very little, and only water when the get really dry. I don't think chopping them off is the best idea. Remember, you can bury the stems when you plant, so leggy tomato plants aren't a total disaster.

Jason

You can go ahead and bury some of the stems now if you'd like. It will encourage stronger root development and also solve the problem of the too-tall stems.