Nothing by David Drake yet?
Besides his
Hammer's Slammers series (sometimes irregular in quality), I recommend
Redliners, where a group of "burned out" front-line soldiers from a war against the aliens is sent to babysit a bunch of "forced colonists".
Another good one is
Falkenbergs Legion, from Jerry Pournelle. The US and USSR join to form the CoDominium, stop technological advance, and set to colonize new worlds.
Also liked two series by John Ringo:
Into the looking glass (and it's space mushrooms from the second novel onward
), and the
"Posleen War series". Maybe too American centered (logically), but fun. I haven't read yet
Watch on the Rhine, where the German must face the option of rejuvenating former Waffen SS troops to fight against the alien invaders. Sounds interesting.
I must mention
Doomfarers of Coramonde too, if only for the rescue mission to Hell.