Humane Alliance in North Carolina is BRILLIANT (see my previous posts on it), but they can have a long waiting list, so I would email them ASAP.
I did the Vets Go Wild course in South Africa, and it was amazing, but is not cheap (a paid placement).
Stapeley Grange is in the UK but is great for wildlife conservation.
I did a placement at the Toronto Wildlife Center and really enjoyed it (in Ontario, Canada).