Weaponsmithing: Just as the name implies, you'll be crafting all weapons with the exception of wands and staves. Since that's everyone except Mages, this will likely be a popular profession to have. If you're taking Weaponsmithing as a skill, you'll also want to take Mining for the ore and Foraging for wooden handles, stocks and the like.
Armorsmithing: Armorsmiths will of course want Mining; Butchery is also very useful for this profession, as it will be used in creating chain armor.
Artificing: The favored skill of Mages, as it's a great source of staves and wands. The rings, necklaces and trinkets are also nice, and all pieces seem to be good sellers in the Auction House. Take Foraging and Mining so you'll have a good supply of ore and wood for your craft.

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Apothecary: Potion brewing players will need the plants gathered from Foraging and items gathered from Butchering beasts. Any resources from these gathering skills that aren't needed can be sold to other players or passed on to alts.
Outfitter: Outfitters craft leather and cloth armor from hides and cloth; since cloth drops off of humanoid mobs, you only need Butchery as a gathering skill. This leaves you with an open profession spot for either Runecrafting or some other skill.
Runecrafting: This profession is the only one in Rift that is self-supplying. Breaking down enchanted items supplies the materials for what you'll create with Runecrafting, which are primarily gear-stat-boosting items. Think of this like World of Warcraft's Enchanting skill.