AMD's HD 7000 series are being released at the moment, the HD 7970, HD 7950, HD 7770 and HD 7750 are already out and the HD 7870 and HD 7850 will be around shortly. They will then be followed by the lower end cards and some kind of dual chip card.
Nvidia's 600 series were due around April to coincide with Ivy Bridge but now Ivy Bridge has been held back until June so who knows when they will release them now. Probably sometime between April and June though.
Nobody knows for sure what the prices are going to be. There has been a lot of rumors going around but nothing I would call creditable. But it would stand to reason that the prices should be inline with AMD's 7xxx series.