I will start with acronyms for coupled-cluster, and someone else might answer with acronyms for basis sets or for functionals or for many body perturbation theory or for composite approaches or for different types of SCF:
Coupled Cluster acronyms
CCSD, CCSDT, CCSDTQ, ... (coupled cluster with singles, doubles, triples, quadrtuples, etc.)
CCSD(T), CCSDT(Q), ... (coupled cluster with perturbative triples, quadruples, pentuples, etc.)
EOM-CCSD, EOM-CCSDT, ... (equation of motion coupled cluster, w/ singles, doubles, etc.)
STEOM-CCSD, ... (similarity transformed equation of motion coupled cluster, w/ singles, etc.)
LR-CCSD, LR-CCSDT, ... (linear response coupled cluster, a synonym for EOM-CC)
CC2, CC3, CC4, CC5, ... (second, third, fourth, fifth-order coupled-cluster, etc.)
SCS-CC2, SCS-CC3, ... (spin-component scaled second, third, fourth, coupled-cluster, etc.)
SOS-CC2, SOS-CC3, ... (scaled opposite-spin second, third, fourth, coupled-cluster, etc.)
BCCD, BCCDT, BCCDTQ, ... (Brueckner coupled cluster with doubles, triples, etc.)
Mk-MRCCSD, Mk-MRCCSDT, ... (state-specific Mukherjee multireference coupled-cluster)
pCCSD, pCCSDT, pCCSDTQ, ... (parameterized coupled cluster with singles, doubles, etc.)
TCCSD,TCCSDT,TCCSDDTQ, .. (tailored coupled cluster with singles, doubles, triples, etc.)
CVS-EOM-CC, .. (core-valence separated equation-of-motion coupled-cluster)
RCCSD: partially spin-restricted coupled cluster
UCCSD: spin-unrestricted coupled cluster, or unitary coupled cluster
RDCSD: partially spin-restricted distinguishable coupled cluster
UDCSD: spin-urestricted distinguishable coupled cluster
pCCD: pair coupled cluster with doubles (sometimes called AP1RoG)
CCSD-F12, EOM-CCSD-F12: coupled cluster, or EOM coupled cluster, with F12 correction.
RI-CC2: coupled cluster, with the resolution of the identity approximation for the integrals.