Where do i start when trying to get webservice API's integrated? I am building a travel website for a client, and we need search form tied to different API's and in some cases combined API's returning results.

I am a seasoned PHP developer, but fairly new to Drupal.  

Where should I start? what modules should i be looking at?

Any help would be great.
There is a very active group of developers working with the Services module. I am sure that another seasoned PHP developer would be welcomed by them.