There's been a bit of discussion in the ol' blog-o-sphere lately on shields, and how to make them more effective. This is all well and good, and I might be trying a few of the suggestions myself, in addition to the ever-awesome Shields Shall Be Splintered houserule from Trollsmyth. Unfortunately, though, unless I get really weird with it, shields are pretty much always going to be inferior to two-handed or two-weapon fighting in D&D, outside of specific, controlled situations.
The best thing a player can do, survival-wise, is to stay out of fights. The second best thing is to make those fights short. Defensive power doesn't really help with either of those goals, unless it's absolutely overwhelming. Offensive power helps with both. It doesn't matter how good your AC, or how much DR you have, if the monster gets a chance to pull something screwy, so generally you're going to be better off figuring out how to deal as much damage as you can in as short a period as you can. Hence: Two-weapon fighting, two-handed weapons.