Android: Gmail's attachment handling on Android is not so great -- it can only view certain types of files, and it won't let you save those attachments wherever you want. Gmail Attachment Download solves the second problem by asking you where you want to save each file you download.
Sadly, Gmail Attachment Download won't help you download ZIP files and other files Gmail blocks, but it will make downloading (for instance) MP3s a bit easier. Instead of previewing the file and throwing it in the "downloads" folder with everything else, just choose "Gmail Attachment Download" as the program you want to open the file with.
It will then ask you where you want to save the file on your SD card and what you want to call it, saving you a lot of hassle with time consuming file managers later on.
Gmail Attachment Download is a free app for Android phones. It won't show up in your app drawer, just in the menu you see when you go to download attachments from Gmail or other email apps, so don't worry if you don't see a shortcut for it.