Craig Booth—who previously made those NFL height/weight charts—just released a great series of graphics showing how the median weights of various positions have changed since 1950, based on data from Pro Football Reference. Booth isn't the first to visualize this sort of trend, but the inclusion of the 25th/75th and 10th/90th percentiles helps paint a clear picture of not just the change in weights, but also the relative variance within each of these positions. Plus, I like his colors.
Below is the complete set of charts. You can also check them out over on Craig's site, where he adds some interesting notes and lists some of the major outliers.
*Recently, Pro Football Reference has started classifying long-snappers as centers.