I have a Seagate FreeAgent GoFlex 1TB external hard drive where I keep a lot of my extra data. Very recently, I can't pin-point exactly when, the hard drive has been causing Finder to crash, most of the time irreparably -- and by irreparably I mean it will crash and I'll try to relaunch it but it won't work, in fact it won't actually relaunch unless I then click the Finder icon (which had no dot under it), after which it will immediately launch into an "Application Not Responding" state.
The reason I believe it is the external hard drive is because I have two computers, both of which have the same problems when doing stuff with the hard drive, and neither have problems when the hard drive isn't plugged in.
Some weird things: I have been accessing an excel document on the drive and have been saving the document this entire time -- before I began to think that it was the hard drive causing these problems. It seems as though I could open that document and save it without any apparent problems. Same sort of thing when I used Ableton Live recently. I could access my sample library on the external drive through Live's browser and it would seem to work just fine. However, with Live, when I tried to save a project it would immediately crash Live (presumably because Live is trying to save via Finder or something?). I can't remember if Finder would subsequently crash or not, but I remember having terrible issues with Finder crashing around the times I would be using Live and trying to save.
I tried doing a Repair Disk on the external through Disk Utility, but after it was showing only the stripey progress bar down at the bottom and only saying "Verifying and Reparing Disk," for a little while I stopped it and tried to quit Disk Utility, only to have Disk Utility crash and now Finder crash as well.
Another couple of things to note. Finder is not able to copy something to or from the external, or move something from the external to the trash. It will be stuck at 0 percent progress and if I press the x it will say "Stopping" and never go away. However when I do that and then just unplug my external I immediatley get a "Disk removed improperly" dialog and Finder will work again right away.