http://www.newegg.com/ProductSort/SubCategory.asp?SubCategory=414
There's the already-packaged external hard drives and many come with pre-installed software for performing back-ups. That pre-installed software is of varying quality.
Ol' Dan has a great idea. Poke around and you can find cases for an internal hard drive you shove the hard drive into, connect a plug, then with the two cables that plug into the rear of the case plug into a power supply and the USB thingy on the back (or front, if there) of your coumputer.
My Win98 SE (later, XP) detected the critter and it worked devinely with no problems. Turn it off and on willy nilly and the E drive letter appears allowing me to access the external drive easily and quickly. I love it!!!! Grabbed a 160 gigabyte drive and back stuff up regularly.
Been using Karen's Replicator for its ease of use and it's FREE!!! Karen's is a reliable well-known site and I've used her goodies off-and-on for a long time. Still, it's always a good idea to run an anti-viral scan on any downloaded goody due to the off-chance a hacker broke in and inserted hostile code(not likely but.....) oh... it's just a good idea to scan everything!!!
Karen's Replicator is good for normal day-to-day file and folder back-ups.
http://www.karenware.com/powertools/powertools.asp
Recommended by the Pricelessware bunch of free software seeking folks:
http://www.pricelesswarehome.org/
(links to many free softwares. archives for previous years mentions)
After reading many reviews by various computer stuff writers (the pros) and reviews by various users I wandered over to Acronis True Image
http://www.acronis.com/
and poked around. Amazon.com had it for a penny less than 40 bux with free shipping so.... wanting to be able to back-up my entire main hard drive with all the operating system etc. goodies on it, I figured I needed to lose a few pounds so could go without a few meals in order to buy the program.
In a few days I will hoist my blubbery body aloft (akin to boulders removed from holes in a side yard or a Rex the Wonder lizard emerging from a drain) and stagger down to the office of post and retrieve the little key within my little rented rectangular receptacle of mail and access the nearby larger receptacle where my Acronis from Amazon will be calling out to me....."Obbop.....Obbop....come and get me you BIG hunk of man) Hope it's a female-type program.
Will waddle back to the shanty and partake of the program, utilizing the external hard drive and achieving, hopefully, back-up Nirvana that results in paroxysms of sensuous delight pervading my innermost essence.
If ye buys an external hard drive and want to attain back-up delight and ye goes with a set-up with built-in back-up software ensure ye checks out some reviews for that software. Accoring to reviews some of those programs are marginal, not user-friendly, have a tendency to crash thine system etc. Others are reviewed as being mighty fine. Of course, what works or doesn't work can vary from computer to computer for various reasons, such as the programs already installed, operating system used, etc.
Good luck!!!!!