Modern Patterns?

Modern patterns do exist but they are very rare and not what you would expect. They are typically planchet tests not design selections so because of that, the default obverse is Martha Washington and the default reverse is a view of Mount Vernon.
http://uspatterns.com/marwasdesons.html

I guess some modern patterns might include the 1974 aluminum cent and the 1964-D Peace dollar?

In 1896 legislation was passed that required all patterns to be destroyed once they were no longer needed. there have been a few "violations" of that rule. Some 1916 dime and half dollar patterns got out as did some the Saint-Gaudens eagle and double eagle patterns. Another pieces that sometimes shows up are the 1942 plastic composition cent patterns, there is a 1942 steel cent pattern,and 1969 GM roller press test pieces. The 1974 aluminum and bronze clad steel cent patterns. There are a few of the Martha Washington pieces struck on golden dollar planchets. these are possibly legitimate patterns, and there are also Martha Washington pieces on other denominations, usually off center that are probalby NOT legitimate patterns but just the result of outside firms that were loaned the dies for composition tests playing around with them. For example there is one on a zinc planchet, but the mint said that no outside firm testing was done on the copper plated zinc blanks. The MW dies used were not cent sized dies. More than likely someone at one of the firms testing the golden dollar planchets used the dies to strike up some blank planchets he acquired.