An Irish Chain is always a good way to use up scrap squares (if you don't mind it being scrappy, of course) - it doesn't use a lot of them in comparison to the amount of backing it uses, but it's a fun little quilt to make. You can use any size square; and use 5 of them along with 4 same size squares of your background colour to make 9 patch blocks. You then need solid background colour blocks in whatever the size of the completed 9 patch. You alternate these blocks and hey presto - Irish Chain.
What it uses: any size square