Astro File Manager
Android phones do a lot of things well, but file management generally is not one of them--at least, not immediately out of the box. Astro File Manager (available in a free, fully functional, advertising-supported version or a $4 Pro version without ads) fills that gap. Astro is a file explorer, archive manager, backup utility, and task manager all rolled into one. It also has optional add-on modules to extend its functionality: Astro SMB Module allows network browsing, copying, and pasting of files on a Windows or Samba server, and Astro Bluetooth Module adds OBEX FTP support for browsing devices and sending/receiving files using wireless Bluetooth networking. Astro is so useful, I recommend it as one of the first apps you should install on your Android phone.
Astro excels as a file manager. You can browse files both on the device and on the SD Card, with an option to toggle between icon and list views. By default Astro hides file extensions--a habit I find annoying. Changing this display option is easy, but the path is somewhat unintuitive (Menu, View, Change View, Set Directory Options, uncheck Hide File Extensions, and then click Apply). You can edit file names, copy/paste, select multiple items, create .zip archives (particularly useful when you need to e-mail several files at once), extract .zip and .tar file archives, and search.
The search function allows for some advanced parameters, including specific folders, subfolders, file size, older/newer than, and exclusion. You get no separate option to restrict your search to specific file types, but you can, for instance, find all the photos on the SD Card just by typing ".jpg" into the search box. Similarly, you can sort files by name, date, size, and type in ascending or descending order.
You can save folder locations as bookmarks; just press and hold a folder for this option. Bookmarks are a real time-saver when you need to find your way back through a complex folder hierarchy in order to locate an important file.
Astro includes a task manger, which it calls Process Manager. In this tool you can see which apps are running and how much memory they are using. You can also kill apps here, which is particularly convenient if an app is misbehaving or slowing your phone down.
Astro also has limited but useful backup capabilities. You can back up all or some of your apps (Market-installed apps only; in my tests Astro was unable to recognize non-Market apps such as Mozilla's Fennec) to the SD Card folder of your choice. You might want to back up your apps for a couple of reasons. First, if you get a new Android phone, you can just switch out the SD Card from your old phone and restore the apps on your new phone without having to download them one by one. Second, if you have an app that you rely on, you can make a backup copy before you update the app; that way, if the update introduces a bug or breaks a feature, you can roll back to the previous version.
Unfortunately, Astro does not back up your phone's settings, home screen layout, gadgets, contacts, or the like. This is disappointing, but perhaps the fragmentation of Android and the presence of phone manufacturers' customized overlays (such as HTC's Sense or Motorola MotoBlur) may make this kind of functionality difficult to implement reliably.
Despite its limitations and its somewhat complicated interface, Astro is one of the most powerful file-management apps available on the Android Market.