Last year we went from Amsterdam to Brugges via Antwerp.
We used thalys from Amsterdam to Antwerp, then changed to local trains on Belgian Rail.
There are lots of websites with lots of prices.
Highly recommend getting tickets as soon as possible; the earlier you purchase Thalys tickets, the cheaper they can be, We purchased ours early enough the difference in price between first class and coach was 5 euros.
We also used Rail Europe for the purchase; we were able to book the entire trip and had our tickets in hand when we left the US.
There are plenty of ways to get tickets, and while this may have been a more expensive way to go (but after researching it all comes out about even financially), we were happy with the service.