This is a (hopefully) complete list of the recoilless guns used by the Wehrmacht, compiled by Antonio Pena with additional info from the other members of the forum.

German Weapons
7.5 cm LG 1.300 (Experimental model. Developed into the LG 1)
7.5 cm LG1 (The first recoilles weapon adopted by the Wehrmacht. First use in Crete in 1.941)
7.5 cm LG 40 (Renamed LG 1)
7.5 cm LG 370 (Experimental version of the 7.5 LG 40)
7.5 cm LG 1.285 Rh (Only one prototype completed in 1941)
7.5 cm LG 1.495 Rh (Experimental model, intended for Mountain troops use)
7.5 cm LG 1.500 Kp (Experimental model, intended also for Mountain troops use)
7.5 cm Ruckstossfreikanone 43 (A lightweight antitank artillery weapon)
8.0 cm Ruckstossfreiwerfer 43 (Under development at the end of the war)
8.8 cm Düsenkanone Marine 43 (Two prototypes built in 1944, not proceeded with.)
10.5 cm LG 40 (A enlarged version of the 7.5 cm weapon (also known as LG 2/K) Made in two versions LG 40/1 with alloy mount and LG 40/2 with steel mount)
10.5 cm LG 42 (A Rheinmetall design, originally known as LG 2/Rh. Renamed LG 42/1 when carriage change to all steel)
10.5 cm LG 43 (Development of the LG 42, but limited service, intended to replace infantry guns)
10.5 cm LG 2.540 Rh (Prototypes built in 1942)
10.5 cm LG 2.550 (Project start in 1942, but not proceeded with)
10.5 cm LG 2.550 P (Experimental adaptation of the LG 40 for use in self-propelled mount)
10.5 cm LG 2 Glatt (Under development by Krupp, firing hollow charge projectiles)
15.0 cm LG 42 (Intended to replace the sIG 33, but project ended in 1944)
15.0 cm LG 240 (Experimental prototype developed with the 15.0 cm LG 42)
15.0 cm LG 292 (A enlarged version of the 10.5 cm LG 42, intended for use of airborne troops)
15.0 cm LG 3 Glatt (Similar to the LG 2 Glatt)
15.0 cm Düsen-Rohr (Intended as dual purpose naval-coastal gun, only one prototype completed)
28.0 cm Düsenkanone Marine 44 (Development started in 1943, only one prototype built)

LG: Leichte Geschütz (Light Gun)