First of all, windows are usually specify a U-value rather than an R-value. U-value is just the inverse of R-value. The higher the R-value the less heat loss/better insulated, and the lower the U-value the less heat loss. Normally a double pane, argon-filled window should be around a 0.37 or so U-value. But obviously different manufacturers, etc can be better or worse. Usually these values are stated on the manufacturers sticker on a new window or can be found on the manufacturers website for each model. I live in a much different climate in Georgia, but I assume heat loss is not a huge concern, but still should consider something well insulated to reduce heat gain as well. Another thing to pay attention to is solar heat gain coefficient in a warmer, sunnier climate. You'll definately want something with Low-E(emissivity). The lower the solar heat gain coefficient(SHGC) the less solar heat it transmits which translates into lower cooling costs. This value should also be found on sticker or literature related to product.
Thanks, that's what I was looking for. I knew that insulation was rated on an R value but for some reason I saw an article that had R value for windows and I thought I was missing something. Anyhow, thanks for the info.