It's really hard to beat the Vittles Vaults (http://www.youtube.com/watch?v=TT4MBlui4gw
) made by Gamma Plastics (http://www.gamma2.net/
). These have a screw-in lid which is sealed by an o-ring. They are bug proof, humidity proof, rat proof etc. I have converted grain that had been stored in one for nearly 5 years. I don't recommend doing that as a matter of course but I guess you could conceivably keep grain that long in them.
I actually bought the first one as a dog food container (which is what they are sold for) and was loading it into the back of the pickup when the light came on. I went back into the Petsmart and bought them out. The larger sized ones easily accomdate a 55 pound sack of malt.
The ones with the opening to the side are great for stacking with your specialty malts but note that if stack them 3 high (which is easily done) and fill the top 2 with too much grain the weight of those will distort the opening on the bottom one and it can be hard to get the lid screwed back in unless you lift the upper ones off which, of course, nullifies the convenience of having the side openings.