The following appear to be OOP at Amazon, CGN and IST:
Atlantis Attacks Omnibus
Captain America by Jack Kirby Omnibus
X-Men (first series) Vol 2 Omnibus
... and these ones look to be next:
John Carter Omnibus
Man-Thing Omnibus
Punisher (Remender) Omnibus
Squadron Supreme Omnibus
Tomb of Dracula Volume 3 Omnibus
Get them while you can!