Model Forum / Radio Controlled / Air Models / September 2006

Modules are indeed a fine option.

Additional options :

27 MHz is legal for both land and air vehicles.

Ditto goes for 50 MHz and 53 MHz (but you have to be a ham radio
  operator to use this band, of course.)

49 MHz is also similarly legal for ground and air use (but the gear is
generally very low end, as you generally pull it out of toys.)

Devices that use 900 MHz and 2.4 GHz are also legal for both land and
air.  The Spektrum DX6 is probably the most obvious and useful example
of something that uses these bands.

Also, if you can find a Sombra Shadow RX, it can be synthesized for
both the 72 MHz and 75 MHz bands.  (I realize that you asked about TXs
rather than RXs, but ...)  This is the only RX I'm aware of with this
option.