Lots of options, but I think many here believe internet direct companies give you very good value for the money.
Axiom and SVS have been mentioned. AV123 is another one. I bought Ascend Acoustics, and like them.http://www.ascendacoustics.com/pages.../spkrlist.html
THe Sierra is "sleek," being a bookshelf size, and if you get three in light cherry (on sale right now) plus 2 HTM-200 surrounds it's about $1400, so you have $600 left over for a sub. Nothing wrong with Ascend's other speakers either, and they are less money.
Although the rule of thumb is you should spend about twice on speakers as you spent on a receiver, because speakers have more impact on sound than the electronics. Since you spent about $1800 on your 5007, that means $3600 for speakers.
Rules are meant to be broken, so you can do what you want. But even without going that high you could do three Sierras, and six HTM-200 surrounds (for the full 9 channels), for somewhere around $1800 or so. Then you could spend about $1000 or so on a really nice sub, like a Rythmik, SVS, or even an Epik. Or buy two slightly lesser subs to better fill your large room, like Elemental Designs, Hsu, Outlaw, or SVS NSD.