If you're looking for options:
* https://www.activecollab.com/pricing.html
* https://asana.com/pricing
* https://www.wunderlist.com/en/pricing
* http://conceptboard.com/plans
* https://www.flowdock.com/pricing
* http://www.thrivesolo.com/
* https://basecamp.com/
* https://podio.com
* http://www.10000ft.com/pricing
* http://cobaltpm.com/
* https://planscope.io/
* https://unison.com/
* http://trello.com/

If you're looking for a flat structure, try Asana. Looking for customized apps, try Podio. Security and conference calls, try Unison. Quality, visual structure, try Trello.

My first four to try in your situation would be Podio, Trello, Basecamp and Asana.