Syl Arena's book on Speedliting is highly recommended. He recommends starting with a 430EX II and a long off-camera cord, if starting with off-camera flash on a budget. (Syl does not like the ST-E2; he recommends the long cord option.)
I was lucky to start with a 580EX, that my wife acquired along with a pre-owned XTi/400D, so I have no experience with a 430EX. I have since added a second 580EX, a Nissin Di866 II, an ST-E2, and a 580EX II. Using off-camera flash does produce much more pleasing results than the pop-up flash! Even when used on-camera, in the hot shoe, however, an EX-series flashgun is an asset, especially if using wide-angle lenses. The angle involved, with a wide-angle lens and the pop-up flash, results in a shadow at the bottom of the image, cast by the camera and/or lens itself.
To be clear, I need the extra power for night shooting, sometimes needing to light a large area. A 430EX II may be plenty of lighting for your needs.
Canon 5Ds R/7D2/7D/5D/40D/1D2N/M3; Nikon F6/D3s/D700/FM3A/1Dx/Coolpix A. Lens selection undergoing changes; some favorites: Zeiss 2/135 APO Sonnar, Canon 100mm f/2.8L Macro IS and 135L, Nikkor 14-24/2.8G and 24-70/2.8G.