Ok, new model. This one is a "good" guy who can mix it up in meelee, at least for a little while. Halfling, CG. 30 point buy = str 8, dex 20, con 14, int 12, wis 8, chr 10. Improve Dex every 4th level.
Feats: 1. Point Blank Shot, 3. Precise Shot, 6. Weapon Finesse, 9. Craft Wondrous Item (to make that Greater Chasuble of Fell Power, as well as other goodies at 12th), 12. Improved Crit (Ray), 15. Improved Precise Shot, 18. Extra Invocation: Warlock's Call.
Skills: Max out Concentration, Intimidate, Use Magic Device. At higher levels, maybe stop improvng Concentration and go for something else, but maybe keep maxing it out.
Invocations:
1. Hideous Blow
2. Eldritch Spear
4. Frightful Blast
6. Replace Frightful Blast with See the Unseen, get Flee the Scene
8. Eldritch Chain
10. Walk Unseen
11. No replacement, get Chilling Tentacles
13. Vitriolic Blast
15. Devour Magic
16. Replace Walk Unseen with Brimstone Blast, get Dark Foresight.
18. Retributive Invisibility
20 Path of Shadow
I would use the vitriolic blast most often, but brimstone blast is a good back up (plus it is cool to be able to start fires from 250 feet away). I was trying to avoid stuff that required chr saves, mostly. Especially once I got Dark Foresight, I would never, ever be caught with my pants down, and always have an Eldritch Blast at the ready. That said, a creature immune to fire and acid and with high SR would be troublesome for me. But every class has some weak spots.
10th: Energy Resistance picks: Fire and Electriticity.
12th. Make a cloak or vest of resistance, gloves of dexterity, maybe bracers of armor?
Oh, and I would suppose that as far as gamer stereotypes goes: The Wizard/Sorceror is the "nuke", but the Warlock is the "Energizer Bunny". Especially once the above gets Dark Foresight, he will never, ever be caught with his pants down, and always have an Eldritch Blast at the ready.