Panasonic G1 ,G2 or G3
I totally agree with the previous comments; the G3 is your best bet and the Pana/Leica 25mm F 1.4 would be the cherry on the cake for your concerts shots. I frequently use my G3 and 45-200mm zoom for low light indoor shots with very good results at ISO 3200 and even 6400. A bit of unsought advice about low light / concert shots:
a) If you shoot JPEG, make sure you have the white balance well adjusted since AWB and preset settings are often not up to the job in complex lighting enironments; better use either the "colour temperature" or manual colour adjustments (using a white card, preferably) to adjust colour balance ... or shoot RAW+JPEG and play with SilkyPix or Adobe RAW.
b) Beware of the autofocus in low light. If you see the lens is hunting for focus, better switch to manual focus; you will see that your % of useable shots will increase.
Oh and one last thing: If you can, buy the G3 without the base - and underwhelming - 14-42 kit lens; the older 14-45 or the upcoming $$$$ 12-35 F 2.8 are much better bets.