Single most important piece of lighting equipment to start with

[AndyNJ]

What would you guys consider to be the single most important piece of lighting equipment I could buy to start with? Budget is $200-300 (very small, I know, but hey, my fiancée and I are saving for a wedding).

Lighting would mostly be used for erotic and nude photography.

Really, the only equipment I have so far besides my camera (Canon) and two lenses is a pop-up flash diffuser and the DIY soft boxes that I made (here). They're not terrible, but if money would be better spent replacing them rather than getting something to complement them, I'd be open to that. However, with my small budget, I'd like to get the most bang for my buck, so my thinking (which is probably wrong ) is that I'd be best off getting a Speedlight 430ex or something along those lines.

[bhursey]

A external strobe of some sort. I would recommend maybe a Nikon sb28 some cactus v4 triggers and a stand and umbrella. You could do that for close to 200$.

You can get kits also..

Strobist 1 light Kits

[OsmosisStudios]

A flash? Depends entirely on what you want to do with it. If it's gonna live on your camera, then any proprietary flash should do nicely (the 430EXII in this case). If it's for portrait work off-camera, Strobist has some excellent stuff.