Party for my Stalker?

I am going to make some assumptions, as your post doesn't explain your playing style. My assumptions are that you want a thief character for locks, etc., but that you do not need to backstab, and are willing to forego traps, etc. (i.e., you do not want a thief like Jan but will "make do" with either Imoen or Nalia). Next, you want a balanced party with at least one arcane spell caster and one cleric. Next, you may be getting tired of Jaheira and Minsc (I don't know this, but your last comment leads one to consider it).

So, let's look:

Keldorn - Tank, plus bonus of true sight and ovepowered dispel -- a must for your good-aligned party. Carsomyr obviously.

Anomen - Assuming you play him right, he becomes a very effective cleric with the weapon proficiency bonuses of a straight fighter. Lot's of people favor the Flail of Ages for him as a main weapon and Improved Mace of Disruption for those special times. Crom will also work later in the game.

Yopsh/Imoen - I'll ignore Yoshimo for obvious reasons. Imoen can be your thief (with appropriate props as needed). She doesn't have traps or detect illusion, but she will nail down the basics for you and your PC can backstab. Imoen is also going to be your main mage. She will use Staff of the Magi and the Gesen Bow (she'll use that other one you get from the Beastmaster in the Coronet until you get the Gesen Bow).

Now for the tricky part. You really don't need another tank per se, as Keldorn and your PC, with help from Anomen, satisfy the job. You may want Mazzy, however, as another second tiered tank and good archer.

Another possibility is Cernd. He's not "good" and forget this if you don't have the mod to rebalance his class. If you do have that mod, he can be fun. You get earlier access to the top druid spells and his shapechange is quite powerful with werewolf and greater werewolf. In a pinch, he can be yet another tank.

If you lean towards magic, you can add Aerie or Nalia. Aerie has the benefit of being able to stack divine and arcane spells in such things as sequencers and the like, but Nalia moves up faster. (My problem with her is that I think she is an Imoen clone. My problem with Aerie is that I hate her whining.)

If you have the Kelsey mod, you can pick him up. He's a sorceror, which is one of my favorite classes.

If it were me, I would go with Cernd and Kelsey.