There are a lot of different kinds of ice cube trays out there. There is the standard cube-like shape from a tray, the kind that comes out of automatic ice makers, long thin bits of ice to fit in your water bottle and many other interesting shapes. IKEA, for example, has had fun ice cube trays for years.
Toxel.com has accumulated a list of 20 unusual ice cube trays from all over the world, most of which are incredibly fun and/or interesting. There are Lego bricks, Tetris pieces, strawberries, letters, even ice-shaped Space Invaders. The article also includes links to sources for the trays. My favorite is definitely the Gin & Titonic (shown) from WorldWideFred, who also makes a lot of the other ice cube trays.
Check out Toxel.com’s list! Maybe your next gathering will be more interesting for it.