The bigger Contax flashes are rather out of scale to a G2, and mostly rare (and expensive if you find them). The smallest swivelling Contax TTL flash is the TLA-360, with which the G2 already is decidedly top-heavy. My favourite is the TLA-280 - it is reasonably compact, can't swivel, but tilt, can zoom, has an integral eye light reflector, second-curtain sync, enough power (GN80), fits many standard white card and balloon diffusors and it frequently shows up on ebay and used camera dealers for a modest price. About the only downside is that it takes rather expensive batteries/rechargeables.
If you go the SCA way, get the latest 300 series Contax foot, the SCA382. The earlier 380 wont do at all, and the 381 is unreliable or (depending on the revision and flash) fails completely. And don't waste money on a 3802 either - its extra features are lost on the G's, as they can't transmit camera settings to the flash.
Sevo