We present evolution models predicting both the radius and effective temperature of the newly discovered extrasolar giant planets (EGPs). Theoretical spectra of 47 UMa b and 70 Vir b, two moderately hot EGPs whose atmospheres are dominated by absorption of water and methane, are compared to similar calculations for the brown dwarf Gl 229 B, and observations of Jupiter. On this basis, we predict that a wide variety of EGPs should be bright in the 4-5 mu m spectral region.