You can use 2.5" squares in Double Wedding Ring arches. I have a DWR template set that fits 2.5" squares. And, if you are really adventurous, you can do Cathedral Windows using 2.5" squares! There is also a book called "Jelly Roll Sampler", or something like that, and most of the blocks in it would work for 2.5" charms. I am (slowly!) working on the basket sampler quilt from the book and only using charms. Just a few ideas.