Brad Brewer posted on Twitter a collection of all the Google Maps Highlight Icons he has spotted to date.

Here is his screen shot, click to enlarge:

Here is the list in text format:

Great Pool
Restaurant
Popular with families
Pet friendly
Great rooms
Fitness center
Free breakfast
Top rated
Popular with couples
Luxurious vibe
Great dining
Indoor pool
Popular with business travelers
Bar
Near public transit
Free parking
Great breakfast
Stylish vibe
Free wifi
Great location
Pool
Air conditioning
Great service

This came up when Sergey Alakov posted on Twitter about new icons he saw on hotels.

Forum discussion at Twitter.