  We show that conditional output measurement on a beam splitter may be used to
produce photon-added states for a large class of signal-mode quantum states,
such as thermal states, coherent states, squeezed states, displaced
photon-number states, and coherent phase states. Combining a mode prepared in
such a state and a mode prepared in a photon-number state, the state of the
mode in one of the output channels of the beam splitter ``collapses'' to a
photon-added state, provided that no photons are detected in the other output
channel. We present analytical and numerical results, with special emphasis on
photon-added coherent and squeezed vacuum states. In particular, we show that
adding photons to a squeezed vacuum yields superpositions of quantum states
which show all the typical features of Schr\"{o}dinger-cat-like states.
