High-Speed + High Power = External Battery
I prefer using Ni-MH batteries in my speedlights. Especially the "pre-charged" ones, because they hold their charge for much longer between uses.
They do a full-power recharge in less than four seconds in most flashes, which means that at, say, 1/4 power, you can shoot away with almost no regard for recycle time. As long as you are averaging about one shot a second, you are fine for moderate bursts.
But what if you want to shoot fast at 1/2 -- or full -- power?
I am a big fan of the Lumedyne rechargeable, high-voltage battery packs. They are not cheap, but they give you the ability to shoot quickly when you need to on higher power settings.
They can charge your flash in as little as 0.7(!) seconds for a full-manual power shot. If you are shooting in fluid situations, and your paycheck depends on those flashes being ready, they are worth their weight in gold.
But you have to be careful -- these batts can deliver enough manual flashes, quickly, to overheat your flash. So work in bursts -- don't just turn on the garden hose or you will pay the price.
The Lumy's I have used (since back when the earth was still cooling) are big and clunky compared to the sleek little ones they have out now. Lumedyne has started a video channel on YouTube, and one of the videos gives a basic run-through on their new, smaller "cyclers".
To use these (or any other hi-voltage batt packs) your flash needs to have a high-voltage socket. I do not use them very often (not shooting to much hoops these days). But when you need them, they are golden.
:: Lumedyne YouTube Channel ::
:: Lumedyne Cyclers Info ::