Due to my previous post, .Net Framework Problem, Please Advise. - Factual Questions - Straight Dope Message Board, it’s been recommended, on and off the board, that I do a complete reformat of my computer. 
So, I’m looking for a portable HD to back up my data (music, divx vids, etc). However, most seem to backup everything and use proprietary software to do it. Are there any reliable HDs (around 250 GB)that let you choose what to save or use drag and drop? Any help and recommendations would be greatly appreciated. 
You could get a regular internal HDD (cheaper than a portable one) and a drive enclosure and use any software you want to do the backups.
Do you have an ipod? I just use my ipod for disk storage. Do you really need 250 GB for all your files? My ipod is only 160 GB and works fine for saving backups of all my setups and pictures and videos you just have to enable disk use in itunes
While it’s true that many portable hard drives come bundled with some sort of backup software, you don’t have to use it. Just about any external USB drive you get is preformatted (usually FAT32 IME) and should appear as a hard drive when you plug it in, if your system isn’t too badly broken. Just copy whatever directories you want.
Many of the new drives come with the installers for their archival software already on the drive, sometimes with an autorun file to start the installer when you first plug it in. You should probably have autoplay turned off (just as a general principle); move the existing installer and documentation files into some subdirectory, or just delete them, if you don’t want to use them.
I’ve used and been happy with these Seagate and these WD drives, though I haven’t done any brutal testing on them (they are just for backups) and I don’t know how they compare to similar versions from other manufacturers. Both of these are one-cable versions, taking all required power from a single USB port; this is very convenient if you’re going to use them often or if you want to use them with a laptop.
I’ve used a WD USB 250GB drive for a year now with my laptop. It only cost c.$50, and I use it for installed games rather than use my internal drive for those. It works just like a regular HDD, drag-drop, etc.
That’s the same one I have, but I got it at a far cheaper price from a department store. I removed all the software that came with it, as I didn’t need it, and reformatted it as NTFS.