The ionization energy (IE), electron affinity (EA) and heats of formation (ΔHf0/ΔHf298) for cyclopentadienyl radical, cation and anion, C5H5/C5H5+/C5H5-, have been calculated by wavefunction-based ab initio CCSDT/CBS approach, which involves approximation to complete basis set (CBS) limit at coupled-cluster level with up to full triple excitations (CCSDT). The zero-point vibrational energy correction, core-valence electronic correction, scalar relativistic effect, and higher-order corrections beyond the CCSD(T) wavefunction are included in these calculations. The allylic [C5H5(2A2)] and dienylic [C5H5(2B1)] forms of cyclopentadienyl radical are considered: the ground state structure exists in the dienyl form and it is about 30 meV more stable than the allylic structure. Both structures are lying closely and are inter-convertible along the normal mode of b2 in-plane vibration. The CCSDT/CBS predictions (in eV) for IE[C5H5+(3A1<-C5H5(2B1)]=8.443, IE[C5H5+(1A1)<-C5H5(2B1)]=8.634 and EA[C5H5-(1A1)<-C5H5(2B1)]=1.785 are consistent with the respective experimental values of 8.4268+/-0.0005, 8.6170+/-0.0005 and 1.808+/-0.006, obtained from photoelectron spectroscopic measurements. The ΔHf0/ΔHf298's (in kJ/mol) for C5H5/C5H5+/C5H5- have also been predicted by the CCSDT/CBS method: ΔHf0/ΔHf298[C5H5(2B1)]=283.6/272.0, ΔHf0/ΔHf298[C5H5+(3A1)]=1098.2/1086.9, ΔHf0/ΔHf298[C5H5+(1A1)]=1116.6/1106.0 and ΔHf0/ΔHf298[C5H5-(1A1)]=111.4/100.0. The comparisons between the CCSDT/CBS predictions and the experimental values suggest that the CCSDT/CBS procedure is capable of predicting reliable IE(C5H5)'s and EA(C5H5) with uncertainties of +/-17 and +/-23 meV, respectively.