A few Themes I've been using lately.
50 Metal or Rock bands or artists, 2 per letter.
60 Hydrocarbons, In 6 groups of 10 Similar types.
196 Nobel Prize Physicists in chronological order. And
81 science fiction Authors.
I generally use the Heavy Metal for bulk freighters, Hydrocarbons for tankers, Physicists for Grav survey or science vessels, and the Authors for Colony ships.
I'm a little dismayed to find that when adding a new theme ingame it's automatically alphabetized. Thats slightly annoying when my physicists get awarded out of order, but its worse with the Hydrocarbons as I had them grouped in a way that made them progress from Solid fuels to Liquid to gaseous etc. VB When Importing names kept the list in exact order.