Google Now has a whole bunch of cards that are not very obvious at first. They only appear when Google thinks you need them most and are mostly based on your searches, current location and calendar entries.
I've only ever seen a few Google Now cards, but that's mostly because the others I would have no use of at all. Here is the list of Google Now cards you can get.
Shows a rough approximation of how far you walked or cycled during the past month.
Displays an interesting fact about your birthdate on your birthday, and reminds you of friends' birthdays.
Shown before your favorite artists give concerts near you, or before other popular events are scheduled near you.
Shown before flights that you've searched for.
Gmail: Events bookings & tickets
Shown before an event booking confirmed by Gmail. After you buy a movie ticket, you get a reminder when it's time to leave for the movie.
Shown before flights confirmed by Gmail or boarding passes received in Gmail.
Shown when you receive a confirmation email and before your scheduled checkout.
Displayed when you receive a shipping notification for online purchases. For some shippers, cards update when the package ships, is out for delivery, or has been delivered. Links on each card bring you to more detailed tracking information.
Shown before a restaurant reservation confirmed by Gmail.
Shows movies playing in your vicinity, and tells you when a movie you're interested in is playing nearby.
Shows updates related to news items you've read recently.
Shown before scheduled meetings.
Photo spots nearby
Shown when you're near a popular spot for taking photos.
Shows nearby businesses and other places of potential interest. If you're at a museum or shop, you can use your camera to look up artwork or get product information.
Gives public advisories for your location from the National Weather Service, U.S. Geological Survey, and similar services.
Shown with relevant schedules when you're near a bus station, train station, or other public transit stop.
Shown when you've searched extensively for property listings and are near a property for sale.
Shown when you've recently used Google Search to research a topic, such as a trip you're planning.
Shown for teams that interest you before, during, or after a game.
Shown periodically for stocks you're tracking.
Shown before your usual commute times
Shows the latest currency conversion information for your location.
Travel: Nearby attractions
Shown when you're near well-known attractions, such as restaurants, museums, and cafes.
Travel: Time back home
Shown periodically when you're in a different time zone than usual.
Shown when you're traveling in a foreign country, to help you translate words and phrases.
Periodically displays current weather and predictions for home, work, or your current location.
There are quite a few Google Now cards as you can see, but you'll probably only use very few. Google will inevitably keep updating the service with more and more cards because they are very useful. Also with all the rumours it's coming to iOS, it'll be a very good alternative to Siri.