When at my local big box hardware store, they've got tons of different types of shutoff valves. Some are called gate valve, others called waste or something similar to that, and ball (I think I can figure that one out), and the list goes on. I really can't remember the name. Anyway, is there a particular type that I need? For me, it seemed like anything that is a "straight through" valve should work right? By straight, I mean it doesn't have an elbow. Maybe I'm making it more complex that I need to. I did try to make sure it said it was for water.

Look here:

Kitz brand valves - PlumbingSupply.com (http://www.plumbingsupply.com/valves.html) under sweat ball valves.

I like the ones at Lowe's better than HD.

You can get them with and without drain ports and those have to be installed in the intended direction. The drain ports are more useful for outside spigot shutoffs. With those, you can shut off the water, remove a small knerled nut and drain the water left in the line that was shut off.

Forget gate valves. New manufacturing techniques for ball valves made gate valves obsolete in the 70's. You would never know that looking at the big box stores. I guess angle globe valves may still have a place where they save an elbow and nipple. So choose a ball valve, threaded, sweat, solvent weld (plastic), or compression, what ever fits into your system and skills the best.

Above 2'', butterfly valves work well, especially with flanged joints.

Look for a valve rated for your application. Often you see 125 psi WOG. That means it is suitale to be used with water, oil, or gas at pressures not to exceed 125 psi. If your heating system is steam, look for an SP rating.

Ok, ball it is then. Good thing I asked since I got the gate type. Looking closely at the valve, not I get why it's called gate. Thanks.

Also, I noticed my old valve knob was blue, which typically in my mind means that it's cold water, which for my case, it is. All the valves I see now are red. Is that OK?

I never paid much attention, I think the handle color is brand thing.