[alex_c]

If you happen to be using Ruby, then Capistrano (http://www.capify.org/) is awesome.

I imagine there are similar solutions for other languages.

Worst case scenario, you can roll your own. A very basic trick is to use symbolic links on your server - deploy the site to a new folder, and simply point the symbolic link to the new folder when you're done.

[lux]

Capistrano works great for non-Ruby sites too! Our site is in PHP and it was easy to get cap working for us. We also use github.com so the site essentially pulls from there, which means we can also rollback in case we ever need to.

[njharman]

Concur, I looked a loooong time for something better then home grown solutions.

Capistrano is great. I've used it to great success deploying Django(Python) apps to complex environments.

[mjnaus]

I second that, some tweaking the recipe and Capistrano does a neat job with PHP sites as well!