Any class would work well with that combo.
With a hunter you'll bring an added level of damage that will be very useful since neither of your friends will output much direct damage, and the quick travel skills they get will prove very useful if you frequently play together.
With a burglar you can crowd control entire groups of mobs with relative ease as well as provide spot healing with fellowship maneuvers.
With a runekeeper you get both a healer or DPS depending on what the situation calls for, but your tank will need to be careful with two light armor wearers in the group. A minstrel is similar, but probably slightly worse off than the runekeeper at present.
A captain could heal through most of the smaller group content fine, with the lore-master debuffs. While being an extra heavy armor class and providing some nice buffs.
A Warden would do well once you gain conviction and would allow the guard to primarily go into overpower mode with a two handed weapon, allowing for greater damage output.
A champion would probably be one of the weaker choices, as while it would provide decent damage and armor, it doesn't bring anything that you don't already have. That said, it's not a bad choice. Having a guard tanking would allow the champion to go all out with area of effect and provide additional safety to the lore-master.
Edited, Nov 26th 2010 10:14pm by Therion11