Reddit mentions of This Is Strobist Info: Your Setup Guide to Flash Photography

You've got two options ... speedlights and studio strobes. Those are the light sources, obviously. For either option, you'll need to pick up light stands, light modifiers like softboxes, umbrellas, or reflectors, battery packs or other power source, and radio triggers.

The link I recently posted was a video of four different speedlight options. Speedlights are the most portable, although they do have less power than strobes. Lots of photographers use just speedlights. There are mounts you can purchase that hold 3 or 4 speedlights on one stand, giving you the option of more power when you need it.

What I use are strobes from Paul C. Buff. I'm completely satisfied with his products. I have two Einsteins, 1 AlienBees Ringlight, assorted stands, softboxes, and umbrellas. I use the Cybersync triggering system of his, and the Vagabond portable battery is top notch.

This is a good starting point. I love the PLM umbrellas, but those aren't as easy to work with outdoors as softboxes. If you do stick with the PLM umbrellas, I suggest getting the soft silver instead of extreme silver. And you can probably get away with just one vagabond power pack, since it has two outlets for strobes.

Also, this is the best single book I've found that teaches off-camera flash. It's all about speedlights and modifiers and is well worth the purchase price.