At the local museum of Sundbyberg you can find old pictures, objects and stories from the town. Unfortunately the open hours isn't the best, when writing this the museum is only open 14.00 to 16.00 on Tuesdays and Wednesdays and 13.00 to 15.00 on Fridays.
The Subway station in Sundbyberg is one of the most art decorated stations in the Stockholm subway network. My favourite is the wall paintings by Peter Tillberg.
Check my travelogue about Sundbyberg Subway art for more photos.
The old water tower in Sundyberg is a rather special building, with a lot of details that you might not find on other water towers. It's left unused since many years, while the community never can decide what to do with the building. One of the good ideas is to make a café in the top of the tower.
The park around the water tower is also a popular place for relaxing, enjoying the sun and watching the great view over Sundbyberg and the surrounding area.
One of the places most worth a visit in Sundbyberg is Auktionshuset (Auction House). Here you can find a lot of old and new things to a cheap price. Each Sunday it's auctions, but during the whole week you can also buy things directly from any stand on the big market floor.
You can find things as paintings, furniture, toys, old records, old magazines and comic books... it can be a long list.
This church from 1892, located in Lilla Alby, is the smallest and in my view the most beautiful in Sundbyberg.
It's though just open on special events, so check the website for more information.