What kind of speakers should I get?

I just moved from a small condominium to a home. I noticed that because of more space, my bookshelf Paradigm Atom Monitor speakers don't sound as full as when I was in a smaller room. My budget is around $500 for some new speakers (maybe a little more to add a center channel). Should I be looking at a floor standing speakers or maybe a better bookshelf? Any help will be appreciated. Thanks in advance.