Welcome to the addiction, it's called Aluminitis.
Now about the models - currently there are three base models:
- flying cloud - lowest price
- international - modern minimilist
- classic - traditional styling, high end wood & upholstery
You can go to www.airstream.com
to get a good overview of the models and lengths. I don't think Flying Clouds go longer than 27', Internationals the biggest is 30' only the Classic goes to 34.
There are also special editions on about everything but the classic - which is also Classic Limited. It might be helpful for you to know that Flying Clouds were renamed from Safari in 2006 or 2007. Internationals were originally called CCD's (for Christopher Deen who came up with the minimalist modern look that sorta shook up the whole RV industry), and Classics or Classic Limiteds used to be Excella's until sometimes in the 1990's if I recall correctly.
Odd special editions currently around - The Panoramic a 34' tri-axle that's designed as a toy hauler. Eddie Bauer in the 25' and now a 27' - also designed toward the younger demographic - toy haulers to carry kayaks, canoes, bikes, etc.
Check the Classifieds right here. There are many good trailers available.