On deck:
Thral'k Kos.
The Concept
Thral'k is a poison dusk lizardfolk in Eberron that is "touched" by fiends. It seeks to master this power in the outside word. In 3.5, he was a scout/warlock combination (due to skirmish/eldritch blast synergy).
Moving to 4E
Another clear Striker. The main question is whether Thral'k is a Warlock or Ranger first. Eldritch blast cannot be gotten except through Warlock, so Warlock primacy it is. We still want a touch of that old "scoutiness", so Ranger mutliclassing is used.
The other big problem is that of race: Poison dusk lizardfolks are not in the Monster Manual (at least, I do not think they are; no MM yet). Looking at the Monster Manual 3, their big things are +2 Con, +2 Dex, poison use, small size, some bonus to athletic-like skills due to their tails, and their chameleon skin when not armored. All but the last is easy to port; for poison use, I just game them poison resistance similar to the Tiefling fire resistance. For their chameleon skin, I played around with various sorts of mechanics (invisibility like the gnome, automatic or large bonus to distraction checks, etc.) before settling on the final racial power.
Poison Dusk Lizardfolk
Ability Scores +2 Dexterity, +2 Constitution
Size Small
Speed 6 squares
Vision Low-light
Languages Common, Draconic
Skill Bonuses +2 Athletics, +2 Stealth
Poison Resistance 5 + 1/2 character level
Chameleon Skin Use chameleon skin as a racial power.
Chameleon Skin (move; encounter)
If adjacent to a terrain feature, conjuration, or zone that could provide cover or concealment, you gain concealment and may make an immediate Stealth check to hide. This concealment lasts until then end of your next turn.
The Conversion
Thral'k Kos Level 3 Poison Dusk Lizardfolk Warlock
Initiative +2;
Senses Perception +1
HP 32;
Bloodied 16;
Healing Surge 8;
Surges Per Day 11
Resist Poison 6
AC 16;
Fort 17,
Ref 15,
Will 13
Speed 6
Action Points 1
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pact blade dagger +1 (standard; at-will) ✦ Weapon
+5 vs AC; 1d4 damage.
eldritch blast (standard; at-will) ✦ Weapon, Implement
+7 vs Reflex; 1d10+6 damage
Hellish Rebuke (standard; at-will) ✦ Arcane, Fire, Implement
Attack: +7
pact blade dagger +1 vs Reflex
Hit: 1d6+6 fire.
Diabolic Grasp (standard; encounter) ✦ Arcane, Implement
Attack: +7
pact blade dagger +1 vs Fortitude
Hit: 2d8+6 damage and slide the target 3 squares.
Fiery Bolt (standard; encounter) ✦ Arcane, Fire, Implement
Attack: +7
pact blade dagger +1 vs Reflex
Hit: 3d6+6 fire damage, adjacent creatures take 1d6+8 fire damge.
Flames of Phlegethos (standard; daily) ✦ Arcane, Fire, Implement
Attack: +7
pact blade dagger +1 vs Reflex
Hit: 3d10+6 fire damage.
Chameleon Skin (move; encounter)
Hunter's Quarry (minor; encounter) ✦ Martial
Ethereal Stride (move; encounter) ✦ Arcane, Teleportation
Eldritch Pact: Infernal Pact
Dark One's Blessing
6 temporary hit points when invoked.
Prime Shot
Shadow Walk
Warlock's Curse
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Alignment Evil;
Languages Common, Draconic
Str 8 (-1)
Dex 13 (+1)
Con 20 (+5)
Int 14 (+2)
Wis 10 (+0)
Cha 10 (+0)
Athletics +2,
Arcana +8*,
Bluff +6*,
Intimidate +6*,
Stealth +9*,
Thievery +7*
* Trained Skill
Feats: Improved Dark One's Blessing, Warrior of the Wild
Gear pact blade dagger +1,
bloodcut leather armor +1,
cloak of resistance +1, other stuff
Thoughts
I'm not sure about my poison dusk lizardfolk: If they are too strong or too weak. Thral'k looses a bit from not being a true "scout", mostly its shifty nature. Thral'k is very much a warlock with a little bit of Ranger flavor as opposed to half-one and half-the-other, but I think it captures the core of the concept. I do miss his huge Hide score, however.
Edit: Included
Nifft's suggestion regarding tweaking chameleon skin.
+12 dagger +2 or 
