Both Metz and Nissin are very good; Metz guns can be a bit simplistic but they are relatively affordable. I would also recommend looking out for a second hand Olympus FL flash on eBay, for example - FL-36 or FL-50. The R-designation of some FL models means wireless remote control compatible. Panasonic doesn't support this mode, but these flash units also have a simple slave sensor for off-camera use built in so that could be useful one day, or if you eventually get an Olympus body (though not an E-PL1 as this doesn't support wireless control). I don't have any experience of the other brands.