Infrared spectra of the weakly bound complexes N2O-He-4, N2O-He-3, and OCS-He-3 have been observed using a tunable diode laser to probe a pulsed supersonic jet expansion. The rotational structure of the bands was analyzed using a conventional asymmetric rotor Hamiltonian. The N2O-He-3 and OCS-He-3 spectra are mostly a type (DeltaK(a)=0) in structure, with very weak b-type (DeltaK(a)=+/-1) transitions, but for N2O-He-4 the a- and b-type components are both prominent. The fitted rotational parameters are consistent with roughly T-shaped structures with intermolecular separations around 3.4-3.5 Angstrom for N2O-He and 3.8-3.9 Angstrom for OCS-He. The angle between the N2O or OCS axis and the He position is about 80degrees for N2O-He and 65degrees for OCS-He. The vibrational band origins are slightly blueshifted from those of the free molecule, with the N2O-He shifts (+0.2 cm-1) being about twice the magnitude of the OCS-He shifts (+0.1 cm(-1)). The results are of particular interest since N2O and (especially) OCS have both been used as probes in experiments on ultracold helium nanodroplets.