Reflectors are pretty easy to come by. You can get a disc shaped 5 in 1 reflector over at B&H Photography for well under $50, or you could easily make one yourself using some foam board and spray paint (it wouldn't collapse though, so you'd be lugging around sheets of the stuff all the time).
What's the big deal then? I mean, if it's cheap, then it'll probably look cheap too, right?
This shot below was done on an overcast day with a reflector off camera left. I couldn't ask for softer, more beautiful light. The reflector basically acts as a fill light to give me some detail in any shadowed areas, and to add just a touch of punch to the shot.
Clouds make for challenging conditions with the reflector, and it can be tough to find where you're actually reflecting. What I tend to do is ask the model to watch the reflector as my assistant holds it until they can see the brightest reflection.
But the fun doesn't stop at overcast days. In fact, I got to the boardwalk a few weekends ago and made use of my reflector on a bright sunny day, which is something I'd planned to do for a while now. When the sun is out like this, you can easily spot the light as it bounces off the reflector, and direct it accordingly. The shot below is the result.
Who said you can't shoot in broad daylight? Note the way that the light is really punchy, vibrant and directional. Reflecting direct sunlight on a 45" reflector (semi-gold side) results in very bright conditions, and this means high shutter speeds, low ISO's. I could have used a softbox for something like this, but the reflector keeps things simple. Very simple. I don't have to worry about balancing ambient and flash, or shutter speeds exceeding sync speeds and on and on it goes...I just point and expose for highlights.
These tools are great but there is one major drawback that I've found: You need someone to hold it for you. You could set up a bracket and swing arm and all that, but you'll be doing all that while your model or subject watches you fumble about with all of your gadgets. It's just so much easier to get a voice-controlled lightstand, or VCL (AKA: Photo Assistant). This way, you can work in either overcast days and clear days while being mobile and very effective.