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We investigate the capacity of various intersymbol interference (ISI) channels with additive white Gaussian noise (AWGN). Previous papers showed a minimum Eb/N0 of -4.6 dB, 3 dB below the capacity of a flat channel, is obtained using water-pouring capacity formulas for the 1+D channel. However, these papers did not take into account that the channel power gain can be greater than one when water-pouring is used. We present a generic power normalization method of the channel frequency response, namely, peak bandwidth normalization (PBN), to facilitate the fair capacity comparison of various ISI channels. Three types of ISI channel, i.e., adder channels, RC channels, and magnetic recording channels, are examined. By using our channel power gain normalization, the capacity curves of these ISI channels are shown.