As stated by others, it depends on what you want. Also the era of the gear you are reclaiming from.
40s-60s - Vacuum tubes, sockets, terminal strips, fuze holders, mica capacitors, variable caps, if-coils, pots, switches, transformers, indicator lamps, neon bulbs. Resistors and other types of capacitors generally aren't worth retrieving.
60s-70s - Discrete transistors, capacitors, resistors, heat sinks, transformers, resonators, pots, switches...
80s-on - SMD resistors, ICs, connectors.
None of these things is going to resell well (except possibly the vacuum tube stuff because collectors), but they can fuel a wide variety of projects and learning opportunities.