Luxray is definitely one of those "I like it but seemed weak" Pokemon. To me that 120 Attack just tells me it's strong. But in OU, although not all Pokemon are armed to the teeth with damaging moves, they are just extremely bulky or extremely fast. Luxray when compared, although it's Attack is respectable, it doesn't make it up for the poor speed... Enough blabbering though- Luxray CAN be used in OU, but need setup badly.
To make up for it's speed, we have three ways:
1. Choice Scarf: Pretty much not the smart choice. Why? Luxray only have one weakness and that's Ground. Should you get locked in Electric type moves you have to switch out, which isn't beneficial for his Attack stats.
2. Quick Claw, although it only has 20% to go first (which isn't much), it doesn't lock you in one move and you can be more versatile. But it's all luck.
3. Baton Pass. I guess it's the only way to go. It pretty much guarantees Luxray going first given foe doesn't use priority. Plus you are free to choose moves, and can hold an item: eg Muscle Band or Life Orb.
For the passer, I'd recommend Scolipede.
So, with the correct setup you're good to go, but for the moves you must have two to make it work:
Magnet rise: eliminate ground type moves for 5 turns, pretty much turns you into a temporary Electric/Flying type. But without Flying type weakness.
Ice Fang: Coverage. That's all it does, but it hurts, for your target.
The rest two slots are free for your choice, but I'd recommend Thunder Fang if you get Life Orb, and Wild Charge for Muscle Band. Of course you can put a Choice Band but that cancels out the need for a passer.
And for the ability, Intimidate and Guts works perfectly- Guts just make you stronger.
Overall: Luxray can be used in OU, at times super effective. I understand people would go you overlooked how weak it is but I use Luxray in OU metagames, and definitely surprised everyone when it went for the kills. And it works best as a sweeper, not a Sp.D Wall.