We are using Streak right now, and it has been the best tool I've found so far - streak.com. Streak is a CRM / Project management tool built into GMail, so you don't need to switch between email and another website to handle communications. Streak has a lot of flexibility to it, but this also means that you need to spend a couple of days customizing it to get it right for your team. I'm putting together a guide now on how we've customized streak for our start up, and I'll send it to you if you're interested. Streak went through YC btw, and their tool is completely free.