If you look at modern world commemorative coins you find that any kind of coin you can think of has been produced. Take coins like the 7 Wonders of the World spherical "coin" from Poland or Somalian motorcycle shaped dollar coins. However, when you look at modern U.S. commemoratives, they tend to be more conservative, sticking to spherical planchets and designs that are typically not the most exciting. However, there are a couple outliers to the trend of United States commemoratives.
The first of these coins is the Library of Congress Bicentennial $10 Bimetallic Coin from 2000. It is composed of an outer ring of gold and an inner disc of platinum. The coin weighs 16.259 grams and has a diameter of 27 millimeters. It is the first and only (so far...) United States bimetallic coin ever produced. The obverse features a hand holding a torch in front of the Library of Congress and the reverse features a modern design of a heraldic eagle surrounded by a wreath. 7,261 uncirculated coins were minted and 27,445 proofs were produced. The uncirculated coins were sold pre-issue at $380 and the proofs at $395. The prices were soon raised to $405 and $425, respectively, after release. They are readily available in high grades with prices ranging from $1,800 the uncirculated coin to $1,075 for the proof coin.
The next "crazy" coin series is the National Baseball Hall of Fame coins of 2014. These were released with much hype and collectors were not to be displeased. The coins have a concave obverse that shows a baseball mitt. The convex reverse that has a design of a baseball with the words UNITED STATES OF AMERICA / E PLURIBUS UNUM and the the denomination. The coins were made in clad halves, silver dollars, and gold five dollar coins. The mintages and prices of the coins vary but most have relatively small premiums over issue price.
Looking towards the future, I like the idea of this trend of unique coiin ideas. However, I think this should be continued in moderation to keep the dignity of the U.S. Mint. There is nothing wrong with being innovative with coinage, but that is not what our mint should be. The Mint should stick to what they do, but keep an open mind to new coin ideas. Only the future can tell what our commemorative coins will be like in a few years.
Yeoman, R. S., Kenneth E. Bressett, Q. David Bowers, and Jeff Garrett. "Commemorative Coins." A Guide Book of United States Coins Deluxe Edition. N.p.: n.p., n.d. N. pag. Print.