W3 Total Cache is a GREAT option! One thing to keep in mind is that you need to individually work with each site for the settings – there is not a global settings area (yet). The next version is said to have this built-in. If you need this “right now”, then WP Super cache does this and is a great option, if you can hold out for a little bit, then W3 Total Cache would be my personal recommendation. Thanks!
