Day trip out of Amsterdam

Delft is closer, easier to get to by train, but doesn't compare to Brugges. Brugges is a long 3 hour drive. Haarlem is very close, if I remember correctly about 20 minutes by train, inexpensive ticket, and has lots to see. Lovely Church with a tower climb, Corrie Ten Boom museum (make reservation ahead of time) and 2 museums worth seeing Teyler and Fran Hals. We enjoyed our day there immensely. Highly recommend it.

I've been to both, and while both are beautiful, Bruges is in a league of its own. However, I wouldn't do it as a day trip from Amsterdam. You will be spending more than 6 hours on the train there and back. Bruges deserves at least one night, if not three! Part of the beauty of Bruges is walking around early morning and evening when all of the day trippers have gone and you can truly enjoy the medieval beauty of the city.

The Markt Square in Delft is wonderful - the architecture is definitely reminiscent of Bruges. You can't go wrong sitting in the square people watching and having an evening cocktail!

Haarlem, as mentioned by Barbara, is also a favorite of ours.

Dawn and Barbara are right: Bruges is much too far away, and there are so many worthwhile things to do just around the corner.
Haarlem is lovely (and indeed just some 20 mins from Amsterdam Centraal), and for some reason I have a weak spot for Leiden (30 mins from Amsterdam).
Hoorn is a beautiful former harbour town, and the trip (30 to 45 mins, depending on the type of train) gives a good view of essential Dutch countryside.
www.ns.nl/en/journeyplanner/#/ gives you the train schedules and ticket prices.

Haarlem is like a smaller version of Amsterdam, wonderful, more quiet (less touristy), but Delft is another world and has the Teyler's Museum! Leiden, a university town, is still another option, with more everyday sites, in addition to an old town, a windmill museum right near the train station, and good people watching from the restaurant/cafe area.

Cleo

Cleo mixed them up - the Teylers Museum is in Haarlem.

Do you have Rick's Netherlands book? In it he has a large number of daytrips from Amsterdam, complete with idiot-proof directions for getting there and back (some involve multiple destinations).

Bruges is simply too far from Amsterdam to be a fun daytrip. It also gets very crowded at the height of the day, so it's much better with 1-2 overnights, or at least as a daytrip from closer places in Belgium.

I preferred Leiden and Utrecht to Delft, but that of course is personal taste. But one advantage of choosing Delft is that you can also see The Hague on the same day.