Those are almost definitely capacitors. I know because we use them extensively in electronics.
The design of the board and position of the capacitors makes be strongly believe that they are simply decoupling capacitors, we put them across the power line and ground on a microchip like this as a filter to get rid of any noise on the chip power supply.
It having been knocked off will not damage your computer unless it tore a bit of track so that the pads are now shorted together. Make sure that the pads are clear. Other than that the worst that would happen is the memory module might "misbehave" at times, though it would be difficult to say how problems might manifest.
The capacitor is essentially an open circuit to DC voltages, but effectively connects high frequency noise to ground. There are generally a few placed close together near any lines that need protection, and loosing one probably won't actually affect the memory module much, if at all, but it might.
In case you care, the little black 8 pin packages at the bottom are 4-way resistor packs, almost certainly terminating the data lines going to the chips.