I stumbled across Command Center by accident and haven’t regretted it a bit.
The premise behind it is an online tool to submit your army list for review by your peers. It also allows you to save and access your army list AND download them in mega-convenient PDF format or print the list out.
Command Center assumes that you have the Codex for your army next to you as you build a list, so it requires a bit of thought and knowledge about the army that you’re building. The great thing about that is that it’s forcing you to know the army you’re building rather than selecting units automatically and without consideration.
You manually enter in the units, wargear, stat lines and costs; the site keeps a running total of the overall points being used.
Think of it like a glorified spreadsheet with features aimed at roster building. There are time saving auto-complete features to quickly enter in units, weapons and wargear but they require you to have entered them previously and saved it in order to be accessible. Auto-complete will only ever use items you’ve saved on your rosters; there is no global library to choose from. Command Center will not save costs either and this is by design for two reasons. The first, again to get you to better learn your army. The second is to abide by Games Workshop’s laws regarding their intellectual property.
Overall, Command Center is pretty intuitive as far as usage is concerned. There is a small learning curve to get used to the interface, but it’s not so hard as to be a barrier.
I’ve used it for a couple of lists (http://cmdctr.net/lists/774 and http://cmdctr.net/lists/785). Community support is great and Thor (the author) is actively commenting on the site as well. From previous forum experience, responses from readers can be “unhelpful”, so a site like Command Center is a welcome change.
You should definitely check it out!