Power Miter Saw, Hand Miter Saw, or Jig Saw?
I agree that for cutting 2 x 4's you absolutely do not want to use a jig saw. While a jig saw is handy to have. As Ed mentioned, you cannot get square cuts and are generally used for thin material and scroll work unless you shell out the money for a professional model with massive power.

A compound miter saw is a better choice than a chop saw. I believe that Ed may have been describing a miter saw but wanted to point this out as they are two very different things.

A chop saw is 'like' a miter saw in that it allows you to make 90 degree cuts in materials but is usually intended in a shop environment for chopping metals.

A compound miter saw allows you to make angled cuts from over 45 degrees to straight 90 degrees perpendicular to the work piece. It also can tilt to make angled cuts at varying degrees. The compound part allows you to do both at the same time. The sliding part allows you to make cuts while the blade slides on a rail allowing you to make wider cuts than a typical miter saw. You can cut 2 x 10's with a sliding version where you could only cut 2 x 6's with a non-sliding version.

You can pick up a very good entry level compound miter saw at your local Lowe's and Home Depot's for around $130 (7 1/4 inch versions - may not handle 2 x 10 cuts). While they have a slightly bigger footprint than your average manual miter saw/box combos you will get much better and lightning quick results. Plus you will find that you can actually do a lot more around the town home with it.

And best of all, these work just as well on the floor as they do on a work bench.

If a small hand unit is all you really want however. Get a power saw (a.k.a circular saw). You will get square cuts (no blade curve) and will take a fraction of the time. Not as accurate as a miter saw but much better for 2 x 4 than a jig saw. You'll save time and have better cuts using a framing triangle with the power saw.

Hope this helps.