Any motherboard that has onboard sound doesn't really need an audio card. Usually the quality of sound from a dedicated audio card will be better than onboard sound but I think for the majority of users it isn't an incredibly large difference. It just depends on what you want to use it for. One thing to consider is that if the onboard sound for some reason doesn't meet your specifications, you can always add the dedicated audio card later. No sense in buying an audio card if you think the onboard will probably be good enough...you can try it and see first hand.
I am buying a new mobo and it has azalia chipset onboard (8 channel sound).
Does this mean it does not need a sound card?