The Fuji X100s seems to be the winner in the APS-C compact arena, but the Sony RX100 is also a fantastic little camera. If portability is the most important factor and you don't want to skimp on sensor size, then I'd also look at the new Nikon Coolpix A as an APS-C option, though it will likely drop in price sharply soon.
If you're okay with sacrificing sensor size, an E-PL5 or E-PM2 with any one of the many fantastic normal m4/3 primes would also work very very well - 17.5/1.8, 20/1.7, or 25/1.4. The 20 is a pancake lens and is quite fantastic, though its AF speed lags behind its rivals. Both the E-PL5 and E-PM2 have sensors very similar to the OM-D; 16mp Sony, 2x crop. They all take very good pictures, and compare very well with Canon's APS-C offerings in ISO performance despite the smaller sensor area.