My setup:

Pally - BS/Eng - I went eng for pulling prior to avenger's shield and then just kept it up resulting in a very nice helm. BS I did mainly for Rune of Warding and Ward of Shielding but have been able to get some nice pieces out of it as well and hope it will be improved in Wrath.

Resto Shaman - Ench/LW - Ench is a no brainer and LW is kind of like BS, it's always nice to know the profession that creates the type of gear you can wear especially with an expansion coming where those professions generally shine at max level before more content is released.

Ele Shaman1 - Alch/Herb, Ele Shaman2 - JC/Miner, Ele Shaman3 - Tailor/Skinner
My thought process here was more from a completionist point of view in that I wanted to be able to make and do everything myself. However, I am in the process of collecting mats to add 3 more LW which will require me to drop Herb/Miner/Skinner and with WotLK I will be dropping Tailoring for Inscription. Though it kind of sucks not being able to collect mats myself, I make enough gold to buy what I need and I don't anticipate that being much differant in WotLK though I may have to wait till 80 to level my professions. However, I have plans to start a second team that will do all my farming but I can't seem to quit playing my current team.