Although CDs can tolerate a fairly wide range of conditions without immediate damage, it is best to store CDs in cool and moderately dry environments. Slight temperature and humidity changes ordinarily do no harm. Fast changes between very warm and wet conditions to cooler and very dry conditions can sometimes result in warping and distortion.

The plastic "jewel cases" provided by many manufacturers and distributors give good protection against scratches, dust, light, and rapid humidity changes. Protect your cased CDs further by storing them in a closed box, drawer, or cabinet. This gives additional protection from light, dust, and climate fluctuations. After using or cleaning your disc, always return it to its case.

Other storage devices, such as zippered cases and sleeve-style holders, provide less but usually adequate protection against damage. Since they can make it easier to keep CDs handy and organized, such storage cases are often worth the moderate increase in risk of damage. When using these cases, be careful to keep them free of dust and debris and, if you retain the literature that comes with the CD, avoid rubbing the play side of the CD across it.

Nearly all damage to CDs occurs when the disc is outside the case and the CD player. Generally, you won't have any problems if the CD is handled correctly and carefully returned to its stored location after use.

Source: http://eil.com/explore/guide/cd_storing.asp