My latest delightful app find is ES File Explorer.
This app improves on the file explorer provided with the Droid by letting you browse or search for folders and files not just on the device itself, but also on the local network, via FTP, and on the Net. It even works as a Dropbox client. Wow. And it's simple to select multiple files, copy and paste, among all of these sources. It can browse or launch viewers of all sorts.
It's additional capabilities are pretty amazing. It can also unzip and zip files, manage apps, and more. I've not yet explored all it can do but what I've tried so far works very well.
This seems to be the best file explorer out there, and It's free, too!