I have the Lee Handheld Autoprime as mentioned above and have been very happy with it, but I barely use it now. I have been using the press mounted that fits the Lee turret press and the Lee Breech Lock Press (and maybe others?). This seems to wrok pretty well. the Large Primer unit works great, the small primer unit used to let primers slide through the slot on the feed tube (i guess thats what you would call it) so I just put a rubber band on it and it has been fine ever since. I like it because It keeps the round on the press so with the turret press I can insert the prepped brass and it doesn't come out until its a completed round. It looks cheap as heck, but so far its held up well and suits my needs.

If your needs require a handheld unit I have been very happy with my Lee Auto Prime.