You're getting a lot of great responses from several well respected posters.
Bob must be too proud to toot his own horn, so I will, GET Bob Gardner's
multiengine text! It's a great book, very down to earth, and very complete.

I did my initial multi training in an Apache (which when heavily loaded on a
hot day will really show you what the second engine is for), created a
partnership that purchased an Aztec (which we love) and did my MEI training
in a Beech Travel Air.

Jim