RC receivers are the main brain behind rc models that control the servos or ESC. For rc receivers to work with ESCs it needs to be fitted with a BEC (battery eliminate circuit).
All rc receivers in this link feature a BEC.
Micro rc receivers are now available which are lighter and more compact compared to the older larger receivers. Measuring only 35mm long x 13mm high x 23mm wide.
Bands currently used: 27mhz AM / FM, 35mhz FM, 40mhz FM
For older receivers a ubec is another method of drawing power from the esc to provide power for the receiver.
How to find out if they will fit your model?
Simple check the crystals or your current RC has the same frequency as described on the receiver. Such as 27mhz AM will only work with 27mhz AM transmitters and crystals.
Secondly please check the connector from the servos and battery connection are a 3 pin type such as pictured below.
02071 Original Standard Size 2ch 2 Channel 27mhz AM Receiver Reciever RC
28463 2.4ghz 3 Channel 3ch Receiver built in Fail Safe
28463 HSP 2.4ghz 3 Channel 3ch Receiver built in Fail Safe
B7011 Micro Mini 2 Channel AM Reciever Receiver 27mhz RC
B7054 2.4ghz 3 Channel 3ch RC R/C Electric Receiver FlySky
HSP 28462 2.4ghz 3 Channel 3ch Receiver built in Fail Safe
RCF31 Mini Micro 2ch 3 Channel 27mhz FM Receiver Reciever RC