MacKay (1997) and Beal (2003) describe Variational Bayesian (VB) inference for HMMs in detail, and Kurihara and Sato (2006) describe VB for PCFGs (which only involves a minor modification to the M-step of the Inside-Outside algorithm).
the E-step for VB inference for HMMs is the same as in EM, while the M-step is as follows: Figure 4: The conditional distribution for state y i used in the Gibbs sampler, which conditions on the states y −i for all observations except x i .