Seriously, there is very little in the way of hi-res sprites. There have been a few attempts at making some of the Doom enemies into hi-res versions. However, most of those looked like ass and were just badly resampled photoshop jobs (though some were pretty good). Due to the work involved, a full set has never been done (to my knowledge). A lot of the pickups and decorations were done for Skulltag and I think those can be got from the ST site. Very few games from the sprite era have hi-res graphics and those that do are quite different in style to Doom (eg Redneck Rampage).
I thought that some of these were quite interesting:http://www.zshare.net/download/61352585aea8cdd9/