How can I identify Lego sets from a box of parts? I am a life long LEGO Maniac, and my kits from when I was a kid were passed down to my nephew, who has just passed them down to my son (40 years of history...).

The trouble is that none of my old plans/directions are still around, and neither are the plans/direction from my nephew's kits. My nephew and I started to do a quick inventory, but he couldn't remember all of the kits that were in the hoard (3 LARGE boxes so far). 

Is there an easy way to figure this out? Does LEGO offer any of their old plans for free online or will I need to pay for them? 

Can any one offer help in identifying some of the fairly recent stuff? I can post images if needed. Some of the newer parts are quite unique.
Your best shot is to identify an individual piece and look it up on Peeron, BrickLink or BrickSet. Since these all carry set inventories, you'll be able to find lists of sets in which the parts can be found. Try to start with more unique parts, chances are they are in a few models only.

Once you're sure you've found a model for which you've all the parts, build it using the instructions from LEGO.com or for older models instruction scans PICSL.

If identifying LEGO parts proves too difficult for some of them, ask experts.