The psyvariars have a lot of deliberate + cool enemy patterns because of the grazing and exploding setups.
I think the strikers patterns are all very good- have to be when the levels are 2 feet long.
Shienryu's got some good popcorn especially later on.
Dodonpachi II-- not good placement by any means, but very interesting-- full parking lots of tanks coming down the screen, or just evenly spaced random enemies filling the screen, all shooting at once.
Does anybody know any pre-Ikaruga era titles where enemies approach from the background to the foreground? Blazing Star comes to mind, but I know there are alot more.