No tablet except the Asus transformer can power a portable hard drive and only through their keyboard dock. Most tablets don't have enough power to turn on large external devices such as an optical drive or hard drive. If you want to be able to connect to those devices then you need to get a usb powered hub or use a desktop external hard drive with its own power supply or an optical drive with its own power supply. The usb port on tablets are only capable of powering flash drives.
I run a tiny 60GB 1.8 inch Hitachi hard drive powered off the Thrive's USB connector only. It is a low power drive, the same kind used in iPods or MP3 players. I "built" this drive by putting the bare 1.8" drive in a nice little case I got on Ebay, for $2.50 plus shipping. I use the ZIF version of this drive, it requires only 3.3 volts, 1.4watts start-up, 1.0 watts read, and 1.1watts write. I usually keep the Thrive on it's charger when using the drive, but not always. Since a USB port provides 5 volts and max 2.5 watts (500 milliamps), this little drive has power to spare.
Here are the specs on this drive, If you are into DIY, it is an easy project, and if anyone wants me to put a "how to build one" video on youTube I can do so.
Here is the case I used for the drive: http://www.ebay.com/itm/ZIF-1-8-HDD-HD-Enclosure-Case-Toshiba-Hitachi-/220594999924?pt=PCC_Drives_Storage_Internal&hash=item335c7c9274
Amazon has a selection of "1.8 ZIF drives" and "1.8 ZIF enclosures". Just search Amazon for either of these phrases. I favor the enclosure I got from Ebay, because it is smaller than most, has a nice gloss finish, and a simple case comes with it.
If anyone has the power output specs for the Thrive's USB I would be interested in seeing them, IE: MAX volts and milliamps recommended? That is the answer to everyone's questions of whether the Thrive USB can handle their particular external HDD or external optical (usb-powered) drive. With that info, I could compare the Thrive's power output to the power specs for your particular USB device
You can use USB media such as flash drives and external hard drives. If you have trouble accessing the media it may be that the media is using an unrecognized file system. You will need to Google that to make sure youre using a supported file system. As far as putting apps on SD, thats not a good idea with this tablet. It has lots of internal storage for apps so to break them in half onto an SD card will only hinder your ability to use all your apps when you want to switch out your SD cards unless you plan to keep 1 SD card in it at all times thereby completely wasting the idea of having full size media slots