Soapstone Ice Rocks – Set of 9 for $5.99 (+$5 shipping – even better deal if you get 2). Chill your drink or warm it without diluting at all.
They hold their temp for 1 hour and are smoothed out on the edges to avoid scraping your dishes.
I’m thinking this would be nice in hot chocolate and soup for my super slow eaters.
Compare on Amazon similar sets for around $15-20.