The most common charger is the Core
UDC20 or
30. The 30 is replacing the 20 so unless its a killer deal on the 20 buy the 30.
The next most common group are
IMAX chargers (B5 and B6) which are basically the same as the Core UDC's internally but in a different case and available via Ebay for a lot less than a Core.
However even this cheap
Fusion will work OK. Its not clever, only does Lipos unlike the others (which is partly a good thing as you can never charge on the wrong mode) and at 3A isn't the fastest, but its 12V and Mains and half the price of a Core