Wav's should be mono, 16 bit, 44.1Khz seems to be the standard around here.
I'm not too certain about the loudness of the samples however - in my experience the best way to produce a sample is to use the maximum amount of headroom without clipping - but this apparently produces sounds that are too loud for some people. I've been told to make samples louder or quieter on a purely subjective basis, even if the actual samples in comparison have the same average RMS some people feel they differ in volume. Personally I'd prefer a standard RMS volume level for all sounds with the game controlling the final mix levels... But since that isn't the case, care must be taken to ensure that a given sample's volume sounds right when compared against all other samples in the game.
For the Ogg format, I use Sony's sound forge to encode a 32 bit 88.2khz wav, and I select the "CD Transparent" preset which seems to work fine- Average Bit Rate of about 96khz.