Class pairing suggestions

I've only recently jumped into 5-boxing, but I've dual boxed a bunch of different combos for about 6 months. With two characters, keep in mind how flexible you want your end-game experience to be. Do you want the option of having a tank, healer, and dps out of two characters? If so, that'll help you in your decision of which two classes to play.
While same-class combos tend to be very easy to play, it's really not difficult to use two classes. I played all of the following to at least lvl 35.. and a some as high as 55.

I started simple - an elemental shaman & fire mage. Both draenei to benefit from the 1% spell hit racial bonus. Both were played as casters, with the shaman going for aggro to take the beating. The mage was more for support..

I also tried a beastmaster hunter & affliction warlock. It was a lot of fun, but the lack of healing was troublesome if a pet went down. I used a carrion bird, and with its screech to hold aggro on AoE, it handled the job well. I'm not so sure it would do as good of a job since the screech-nerf patch.

A rogue and druid was fun - stealth for world PvP was a nice bonus, but mostly it was the rogue dps/tanking and the druid backing up for heals and some dps/CC. This combo is not good for more than 2-3 mobs at a time.. the rogue takes too much damage.

A warrior and paladin were good - arms/fury warrior for the dps/tanking and holy paladin for healing/buffs. However, this combo was probably the most boring of this list for me to play.

My favorite combo so far has been the paladin/mage. The prot-AoE spec paladin was very good at pulling in large groups of mobs and maintaining health while the mage would flamestrike & blizzard the whole group. Not to mention the fact that once you're 70, you'll have the ability to spec full tank or full heal paladin at end-game, while also having a prime dps'er in the mage. The real challenge is having to mouse over to the mage for targeting the spells. Since it's only two characters, and the paladin doesn't take a lot of work to hold aggro, it's not too hard. I wouldn't try this sort of combo in a 5-boxing party unless it's a paladin and 4 mages, and the mouse input is broadcast for the mages to simultaneously target and cast spells.

This is coming from someone who only played two rogues to high level before starting a dual-boxing setup..

A friend of mine used to play two rogues - his main as a seal fate/dagger and 'follower' as combat swords. Since combat swords doesn't require positioning behind the enemy, it worked out better than expected..