Like an SLR, the Panasonic G2 also has a dedicated hot shoe for mounting external flash units, like Panasonic's DMW-FL500, FL360, and FL220. Olympus flash units such as the FL-50, FL-36 ...
One of the main design changes in the Olympus E-PL1 as compared to the original PEN E-P1 model is the addition of an accessory port, much like that featured in Panasonic's Lumix DMC-GF1.