With Duo you gotta ask yourself alot of questions still.
I'm guessing you're going PVE, so I wont even get into PVP but there's a whole lot more information to take into account there.
Now the big question is - although you're going to be duoing, would you rather just stay duo or would you rather take your duo team and start groups.
If you're looking to be the base for a 5-6 player group, I suggest you play the part by playing a Warrior/Crussader and a Cleric/Druid (not shammy - Don't get to pissed off yet shammies.) My girlfriend and I play the Paladin/Warden set, and its AMAZING for basing groups. I know shes competent, she knows I am. We are then free to not worry about 2 tanks, 2 healers, and all sorts of extra safety nets. It also means that we can add essentially any class we want - including 4 more DPS which ends up being alot of damage!
If you're looking to strictly or at least more commonly duo, however, you're going to want more bang for your classes. What the Tank/Healer class obviously lacks in a duo situation is DPS. But you're still going to need someone/something to take the hits. There are many ways to handle this, however, and many of them do not require you go down the standard road.
Ideas for Class combos
Conjuror/Necro + Druid = Pet Tank, 2 DPS Classes when needed, an Evac, a rooter/snarer, Heal(s) in general AND for the pet x2. Fury INT buffs help tremendously for the Caster, while Warden defensive buffs help protect the pet even more.
Rogue + Shammy = Slows and Mitigation Buffs along with Stat/ATK debuffs which can essentially make the rogue a tank. Ability to do massive burst damage between both. Heals/Wards, rooter(if Good), snarer. Excellent agro coopperation means intentional splitting of tanking (a buffed Shammy can actually tank a debuffed enemy quite well.)
Wizzy x2 = Obvious DD destruction. 2 Snarers, 2 Rooters, and ergo the ability to stay out of harms way twice as well and deal twice the damage. As obvious as it sounds this combo works well.
Gaurdian/Zerker + Warlock = Works great against larger encounters, unfortunately these usually give less exp than the solo yet higher encounters. This team can work well, though, at keeping agro and doing massive Encouter/AE damage without a need to heal due to quick slay times.
Fury + Wizzy/Warlock = Have a healer, have excellent complimentary buffs. Have ability to greatly boost resistances for caster battles and have double the rooters/DPS. Also have SoW~
Trust me, there are MANY more, but some combos do not work so well.
Your Warlock specializes in abstract damage and damage to Encounters. While this has great potential at doing massive amounts of damage with extremely good efficientcy, it will not match up to the playstyle of your Cleric. As stated above, the Cleric's AC is not meant to purposefully tank, but merely to be able to withstand an assult better than the other priests. What you'll have is either taking single mobs with Root tactic and having the Cleric do horrible DPS and no healing, or have the Lock tanking encounters with Cleric on heals scrambling as the Lock spams massive amounts of fizzles/interupts.
Please don't let my post discourage you from what you want to do!! Lock/Cleric can make a mighty good base for a group, and I'm sure has potential as a team. But for all intents and purposes, if you're looking specifically to make a duo team, they don't match up as well as alot of other combos.
The best way to think for yourself on this one is to think of a few things.
1) Is there a tank (not necessarily a Fighter just someont to take hits and keep agro)? If not, how will the mobs be kept away from the damage dealers? If so, how will the tank be healed/kept alive?
2) How will damage be dealt to strong single enemy encounters? Can your team root and shoot from afar, or does someone need to be up close to melee? If you have a meleer, are they strong enough to withstand a H^^^'s blows with whatever healer you have?
3) How will damage be dealt to weaker multiple enemy encounters? Is there a way to manage more than 1 enemy at a time? Do you have a tactic to trap/snare/root them all, or is there some sort of tank with AE Agro?
4) How will you get around? Do you have an inviser? A tracker? Speed boost? Evac? Feign Death? What other spells and techs do you think you would want?
5) Do your buffs compliment eachother's classes? Some classes buff for Mit, others for HP, and others still for avoidance. Some buff for INT while others WIS. Remember that while its nice to boost a stat for a player, its almost always best to be able to boost what they are best at! Giving a Monk an extra 10% avoidance is much more effective then upping his/her mitigation by even 20%. Giving a Conjurer a Wisdom/Pow buff helps, but not nearly as much as a INT/Pow buff. See if you can find any killer matches!
Edited, Jun 15th 2006 at 4:26am EDT by tzsjynx