A lot of the new sewing machines have nice large harps that accommodate quilting but they are not cheap. They are also a bit more difficult to wrangle a large quilt through and it is more difficult to do ruler work on them. I have a Baby Lock Crescendo that I use for some quilting and I have a Sweet 16.
As already stated, there are straight-stitch machines with a larger harp space but you still have to wrangle the larger quilts through the opening.