Two kinds of stretching are good: stretching as you strengthen (same session, after doing the lift you stretch the same muscle) and stretching alone (but still working the strength, but without weights).
We NEED to stretch. Modern life makes our bodies age before their time, and we have given in to it. Body building, with its emphasis on the externals (17inch arms etc), can
actually make things worse if it is done without an emphasis on balance of muscle groups and lengthening as well as thickening the muscles. So, do both.
BTW beware of doing your main stretching at high temperatures (sauna etc). Believe it or not there is a right and a wrong way to stretch and the sauna can sometimes lead you to overstretch.