Been spending a lot lately to finish expanding my other 3 character's houses (one room left on my 4th character!), and on a few pwps here and there. I tend to spend the most on furniture (for all my houses, museum and filling out my catalog) and on clothes :3
I tend to share whatever bells I get with my son, I have used the majority to pay off my house (just finished) now I'm using it for PWP's or buying things from Gracies shop.
I use quite a bit on online trading too
I use my bells to upgrade my house and building pwps. After that I spend it on cataloging and after THAT I put it away for savings so I can save to get myself that saving badge! Oh and I also buy gardening supplies but they arent that expensive
Public works projects. I also like to try and buy gifts for my friends such as gorgeous and sloppy furniture. One of these days I plan to get villagers I love too.
I use everything for house expansions, PWPs and buying things from the shops on Main Street. If I had more Bells, I'd use them to buy things from the forums.