I'm a big fan of Clio and MyCase. They're cheap, cloud based, and have gCal integration. Plus you can organize your case files, billing, contacts, etc. all in one place.
Smokeball is another calendaring and document management system I've been playing around with. It's windows only, but great for automating forms if that's your thing. The reminder and calendar functions are also decent.
However, one of the most successful firms I worked for used Google Calendar and a simple cloud based to do list. When a trial was set, we had a prewritten checklist of the dates to put on the calendar and the to do list. Things like: trial memo due date, when subpoenas go out, when discovery is expected to close, etc. We then had weekly staff meetings where everyone in the office attended and we go through the next month of calendar entries and the to do list. When an item/entry was called out, the person responsible would speak up with an update on the progress.
It's not very cutting edge, but in a medium sized office it's the best system I've come across.
EDIT - I never do links properly.