Yes, I'm on a roll with adding new options for David Pulver’s Modular Mecha (Pyramid volume 3, issue 51).
Chemical Rocket: A simpler and lighter design than a nuclear rocket, but less fuel-efficient. Performance and endurance is the same as standard jump jets (they use a smaller motor and carry more fuel), but the mecha gains the Fragile (Flammable) disadvantage, and each extra tank of fuel adds only 40 seconds of endurance (800 yards/second ΔV). However, the exhaust is cooler and not radioactive. Reduce exhaust damage to 6d and the bonus to detect it with infrared to +2.
Ducted Fan: Requires no fuel and has a cool exhaust (damage becomes 3d crushing dkb, no bonus to detect with infrared) but needs a lot of power and only works in an atmosphere with density of 0.1 atmospheres or greater. Move is the same as standard jump jets, but treat each second of use as one shot from a beam weapon.
Fusion Rocket: A weaker but more efficient nuclear rocket only suitable for space travel. Gives 0.09 G (1 yard/second²) acceleration and 5 miles/second ΔV. Each additional fuel tank adds another 20 miles/second ΔV. Use Piloting (Low-Performance Spacecraft).
HEDM Rocket: High-Energy Density Materials are highly unstable, but give better fuel-efficiency than conventional chemical rocket fuels. Performance is the same as standard jumpjets but endurance increases to 80 seconds (1,600 yards/second ΔV) and each extra tank of fuel adds another 120 seconds (2,400 yards/second ΔV). The exhaust is no cooler than that of a nuclear rocket, but isn’t radioactive at least. The mecha also gains the Volatile feature without any reduction in DP.
Jet Engine: A turbojet with afterburner is heavier than a nuclear-thermal rocket of the same thrust, but more fuel-efficient. Performance in air is the same as standard jump jets, but endurance is increased to 5 minutes and the exhaust has the same benefits as that of chemical rockets. The mecha gains the Fragile (Flammable) disadvantage, and can only fly in an atmosphere containing oxygen with at least 0.1 atmospheres pressure. Each additional fuel tank adds 20 minutes endurance.
Nuclear Air-Ram: Although barely capable of take-off in standard gravity, and useless anywhere without an atmosphere, this gives an endurance of one year! Reduce air move to 12/48.
Note: the numbers given are only somewhat consistent with those in sources like GURPS Spaceships and GURPS Vehicles, and weren’t really checked carefully. In the kind of cinematic setting which flying mecha are expected to exist in, this shouldn’t be too much of an issue. Back-of-an-envelope calculations suggest that the existing jump jet rules are extremely generous. A more realistic (and still fairly generous) take would reduce air move to 12/48 (nuclear air rams would drop to 7/36, making them incapable of vertical take-off on Earth).