The best tool I know is mass optimizer. Not only it lets you batch edit exif but it inserts a spinnable article on each photo along with kws and location.
I use that tool every day.
That being said... if you have photoshop you can record an action (add kw, metadata, save as jpeg) and then batch apply that to multiple images.
I also have a question.
Does anyone have a list of the photosharing sites that keep the metadata, location and exif? Most of the big ones except for flickr strip it off.