Project Management Software

My company is in the market for some online collaborative project management software. Since I have never used any of it, I'm appealing to you, the reader. What do you use (if anything) for this? 

I've used Microsoft Project a very small amount, and the open source solution Planner a bit more, but neither are web based or collaborative.

A quick search on Freshmeat returns a lot of likely candidates, but I think we're looking for something commercial, for the supported aspect. On the down side, this will cost the company a certain amount of money every month. On the up side, I think they're finally realizing that my time is finite.

Here are the options we're looking at:

Basecamp

• http://www.basecamphq.com/
  
• $149/month for unlimited projects and users
  
• 50GB

goplan

• http://goplan.info/
  
• $100/month for unlimited projects and users
  
• 25GB

Liquid Planner

• http://www.liquidplanner.com/
  
• $300/user/year
  
• 50GB

Intervals

• http://www.myintervals.com
  
• $175/month for unlimited projects and users
  
• 5GB

DeskAway

• http://www.deskaway.com
  
• $99/month for unlimited projects and users
  
• 25GB of storage

WorkZone

• http://www.teamworkzone.com/
  Their pricing is not published online, but we got quoted $300/mo for 15 users and 3GB of space

Anyone have any experience with one (or more) of these, or any others? I'd be very interested to hear your thoughts.