Okay, why is it some photographers sound so proud when they tell me they never use flash? Flash is not the tool of the devil, people. It's a really handy photographers tool, if you consider yourself to be a professional photographer then you darn well better be able to bust out some light when needed. It's a real dogfight out there these days and if you want to survive then you had better be able to use your tools. I have several images in my portfolio that I used a flash or strobe and I'll bet you wouldn't be able to pick them out. The light is subtle but essential. If something looks "flashed" then you're doing it wrong. You don't need to spend thousands on studio lights or monolights, most of my stuff is shot with shoe flashes, even the architectural stuff.
I had to shoot a mall in Houston, no real budget for an assistant, they could barely afford to hire me. :) I flew out with all my gear as carry on, no time for the airlines to lose luggage, this was an in and out in one day job. So I threw in a couple of shoe flashes and some off camera cords. No light stands, no room. Most of the mall was fairly well lit and I was able to shoot ambient, but there was one shot that just didn't work, the guest services kiosk was too dark, no light near it and bright lights behind it. I really wanted that shot, so I grabbed a flash and held it up and out. Just enough to put some light on the front of the kiosk and balance the other lights. I had the tools to do the job. It's one of my favorites from that day, I like the motion blur of the woman behind the desk.
tutorial on using flash and lighting techniques.