Take a look at the weapons you can make from blacksmithing that are BOE. The small handful that are worthwhile take insane amounts of materials. Generally speaking you won't get these mats from simply leveling, you'd have to go far, far out of your way to aquire all materials just to make an average weapon that's no better then a random BOE blue. There are maybe 2 exceptions in the 40s/50s, but by that time you're getting close to Outland and the first quest in the zone will give your warrior friend a huge upgrade over whatever he's using (unless somehow he raids some level 60 content and gets a quality epic one..unlikely).
As stated above, to really help your friend gold is a better bet. Buy him a BOE blue weapon every 5 levels, maybe throw fiery weapon enchant on it or something. Or if you have an 80, run him through dungeons. Warriors especially are very gear dependant while leveling, weapon especially. You can get by with less, it's just slow/annoying. Heck you can level through this entire game using nothing but white gear sold from vendors, weapons included. But obviously it's not the smartest thing to do.
Blacksmithing is a good profession at 80 for the bonuses, you can put 2 empty sockets in your gear (bracers and gloves) and use whatever gems you like in there. Which is nice if you want to stack agility, most of the other professions give a static ~80 attack power bonus so at most levels 40 agility (2 epic gems) is slightly better. But that's kind of min/maxing, stuff that gives you +10 dps when you're doing 5000+.
Almost any profession is viable for any spec since they all give bonuses that are near equal. I'd go with herb/alchemy, it's easy to level, makes lots of gold. At 80 if you want to min/max you can eventually drop herbalism for something else. Your friend can go mining/skinning since he's new to the game and this will make him lots of gold which he'll need. Alchemy is probably the easiest crafting profession to level. In Outland I recommend you do the quest to become an elixir master, it helps with making gold at 80. Now that alchemists can make 1 epic gem per day, transmute spec may be viable as well.
edit - you asked about PVP daggers at 80. There is 1 dagger blacksmiths can make, the titansteel shanker. It is BOE, you can have any blacksmith make it for you. And now you can run heroic TOC to get better daggers. I wouldn't bother with blacksmithing. If you're very serious about PVP, level engineering for rocket gloves, but have fun being broke all the time =)
In my opinion, ideal PVP professions for all classes are engineering and blacksmithing. Talk about painful to level. It could easily cost you 7500g to level them at 80. Or countless hours farming your own ore (100 hours?). JC'ing is nearly as good as blacksmithing, but it's almost equally as expensive to level. But I really wouldn't worry about ideal professions until well into high ratings. If you start hitting 2000+ and you think a little extra AP and rocket gloves can take you to the next level, that's when you do it. You don't bother min/maxing just to gank random people in BGs...unless you like having no gathering professions and spending thousands for a slight benefit.
Edited, Oct 13th 2009 1:07pm by mikelolol