If you're only considering new cameras, I'd say the Pentax K-x. It's a DSLR, but like all entry level DSLR's, it has an Auto setting. You could get a Canon XS, a NIkon D3000, or an Olympus or Sony. But the K-x is probably the best buy.
If you think a DSLR is too large (the Pentax is quite compact for its type), you might consider an ILC camera such as the Olympus PEN E-PL1, Panasonic G10, or Samsung NX100.
The compacts you have looked at are just above a regular compact in terms of low light ability. They have a slightly larger imaging sensor and a brighter lens. But the sensor is still tiny, so they won't perform as well as a ILC or DSLR. If you're intent to stay with a compact, the others worth looking at are the Canon G12 and the Samsung TL500.
What's the best camera for shooting in poor light? Using a flash or a tripod is not an option. I'm looking for under 500$, and shooting on the AUTO setting.
Right now, it looks like it'll be a Canon Powershot S95 or a Panasonic Lumix DMC-LX5.