I'd like to see a few ramjet engines that need to be going above a certain airspeed to produce thrust but which unlike @8bitsblu's Instell scramjet engines, can provide thrust at speeds below 900 meters per second, and also unlike his scramjets, can accelerate a craft from slower speeds starting in the thicker air of the lower-atmosphere. And before you say that's not a ramjet, I present to you, the work of René Leduc, designer of the O.10, the first ever aircraft to be propelled solely by a ramjet engine. Yes, it had to be carried aloft piggy-back style atop another plane, and air-launched, the O.10, and all of Leduc's ramjet-powered aircraft to follow, the O.16, and the O.21, all spent 100% of their flight-time at subsonic speeds.
The O.10 and the O.21 wikipedia pages for your perusal.
A few higher-speed ramjets to bridge the gap betwixt these and the hypersonic scramjets would make for a way to potentially get into orbit using only air-breathing engines from the launch-pad until entirely out of the atmosphere.