I agree, you should use some "L" shelf brackets UNDER the shelves to the vertical supports. There are many you can chose from, but even the cheap gray 10 inch ones would work fine. Remember, if you use 3 supports, the load is divided, so each bracket will only be holding apx 1/2 of the load resting between two supports. If you mount them over the shelf, rather than under the shelf, the load will be supported only by the mounting screws rather than transferring the load to the upright post, for that reason, I'd stick with mounting them under the shelf. Your shelf as pictured without braces will most likely split at the line where the mounting screws are, as the grain of the wood follows that direction.
BTW, nice workbench! Good luck
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.
Best Answer
Looks like KV shelving. Try KV #182. They come in various lengths and colors.