One of my major 2010 WoW goals is to have all professions maxed. I figure I'm not the only person who wants to do this, so I though today I'd talk about some addons that might help you get there.
First off, Altaholic. It's not just for profession leveling, but it's really useful for it. I can mouse over something in my inventory and see if an alt or a gbank has some and what alts know the recipe and what alts can learn it. I cannot recommend this addon highly enough, especially if you're trying to keep track of multiple professions on multiple alts.
Second, Gatherer and the wowhead database plugin. Every node wowhead knows about, all displayed nicely for you. Great for leveling or farming.
Third, Auctioneer. Okay, I know you're going wtf, but follow me on this. Not only can you make sure that you're buying and selling mats at a good price, you can also use the Snatch list to grab needed items when they're cheap. Just go look at a profession leveling guide (like this one), see what you're going to need, then add it to the Snatch list. Sadly the only way I've found to add items to my snatch list is to have one in my inventory, but I may be missing something. Plus, while you're there, do a vendor search and grab everything that people are selling below vendor price. Vendor them and yay, instant gold!
Other nice addons:
You need to have a character in the mid60s or so to get their professions to 450. If you don't have enough high level toons, may I suggest a couple of nice leveling addons?
Tour Guide and Jaime's Leveling Guide I've been using these for the various alts, and it does make leveling quicker.
Oh, and one last thing... Cartographer. Sadly 3.3 has borked this addon, but if you disable the look and feel module it still works. If you'd prefer to replace it completely, hit No Stock UI for a nice writeup of your options.