The days of melee being "harder" to box are over in my opinion. I would pick ranged / ranged or melee / melee personally but others are boxing 1 of each fine. Think about the following

A) What really sounds cool / fun to play? This should really be the most important thing at the end of the day
B) Utility. Having 1 class that can heal / rezz is awesome. Mage ports can speed travel a lot. Etc etc.
C) Synergy. Having 1 class that buffs casters and your 2nd class being melee isnt optimal. See A though, this should really be less important than A.
D) Once you get to 60+ and start doing TBC / WOTLK group quests etc, having somebody who can take a hit will be nice (i.e. read plate wearer).

If you want a warrior I would pair him with an enhancement shaman. The shaman can rezz, heal, drop awesome melee buffs, melee himself. Also if you get later into the game the shaman gives you a lot of options with dual spec.