Standard 22 point buy, PHB races, Heroic Tier. (sorry) I know halfling would probably be the best, just don't particularly like the flavor of them. I would still be interested in the halfling builds people come up with, though.
I'd recommend either Halfling or Human. Halfling to start as Warlock, Human to start as Rogue. I'm going to stick to PHB at this point and avoid Martial Power and whatnot
Halfling Warlock
Str 10
Con 12
Dex 18
Int 12
Wis 8
Cha 18
Feats
1 Defensive Mobility
2 Sneak of Shadows
4 Novice Power
6 Weapon Proficiency: Rapier
8 Nimble Blade
10 Adept Power, swap Nimble Blade for Acolyte Power
11 Twofold Curse
Powers
1--Eldritch Blast, Eyebite, Witchfire, Curse of the Dark Dream
2--Ethereal Stride
3--Otherwind Stride(You really want this)
4--Swap Witchfire for King's Castle(without Artful Dodger, Positioning strike does little)
5--Crown of Madness
6--Fey Switch
7--Mire the Mind(this is nice on you)
9--Curse of the Black Frost
10--Warlock's Leap, swap Fey Switch for Slippery Mind, swap Curse of the Black Frost for Deadly Positioning
11-Paragon multiclass into Rogue, swap Eldritch Blast for Sly Flourish, take Rogue's Luck
Human Rogue--edited stats, between Nimble Blade and a Dagger, you can benefit more from 18 Cha than 18 Dex
Str 10
Con 13
Dex 16
Int 11
Wis 8
Cha 18
Feats
1 Backstabber, Pact Initiate
2 Nimble Blade
4 Novice Power
6 Action Surge
8 Acolyte Power
10 Adept Power
11 Weapon Focus Light Blade
Powers
1--Deft Strike, Piercing Strike, Sly Flourish, Positioning Strike, Blinding Barrage
2--Tumble
3--Bait and Switch
4--Swap Bait and Switch for Otherwind Stride
5--Clever Riposte
6--Slippery Mind
7--Sand in the Eyes
8--Swap Slippery Mind for Fey Switch
9--Knockout
10--Close Quarters, swap Clever Riposte for Crown of Madness
11--Paragon into Warlock, swap Piercing Strike for Eyebite, and take Mire the Mind as an encounter.