We have been using this for a few months now, with about 30 users. It works really well!
OneDesk is social software that allows you to connect with your customers, employees and business partners and get them involved in the product or service development process. It consists of a unified suite of applications that incorporates social media monitoring, feedback management, idea management, customer service, requirements management, and project portfolio management. With OneDesk, you will build the right product or service faster and more efficiently.
Wrike is very fast, has excellent Gantt charts, tasks can belong to more than one project, has a 3-pane display, email integration, and collaborative editing of task descriptions using EtherPad