[geowwy]

Folksprak is another one like Interlingua, except based on the Germanic languages. One of the nice things about being an English speaker is you can pick up both pretty easily.

Another interesting one is Uròpi which tries to go back to the Indo-European roots of all European languages. It's not as immediately readable as Interlingua or Esperanto but not too bad either: http://uropi.free.fr/comparaisons.html