Another varient is the RBM where the visible units are Gaussian while the hidden units remain binary:

$$ E(\boldsymbol{x}, \boldsymbol{h}) = \sum_i^M \frac{(x_i - a_i)^2}{2\sigma_i^2} - \sum_j^N b_j h_j - \sum_{i,j}^{M,N} \frac{x_i w_{ij} h_j}{\sigma_i^2}. $$