Bake Up a Storm
Bake your best batch of cookies and write little notes on each, giving him hints that you would like to go out with him.
You might try something like, "Me + You = Saturday?" Whatever you do, be creative and make him laugh; that will always get a guy's attention. You could even try making a carrot cake or carrot-shaped cookies and include a note that says, "If you carrot all, you'll go out with me. "
Steal His Jacket
Take his jacket and leave a note in its place.
Write something on the note like, "If you ever want to see your jacket again, then meet me at [so and so] restaurant. " Leave a number for him to call in case he isn't up for it, and offer an alternative way for him to get his jacket back without any feelings getting hurt.
Brown Bag It
Pack him a lunch or offer to switch lunches.
If this doesn't work, trade lunches with him without his knowledge. Include some of his favorite foods in the lunch that you prepare for him, if you know them. Slip a note in his lunch asking him out. Use a little humor, and you can purchase a small note card so that you don't have to be too creative with the design. Sign your name and cross your fingers.
Send Him on a Scavenger Hunt
Use tiny note cards or sticky notes to lead him through the scavenger hunt.
On the last note, ask him out and tell him where to find you. Jump out and surprise him when he finally does find you, and ask him again if he would like to go out with you. Sending your crush on a scavenger hunt might freak him out a little if you don't know each other that well, so this is better-suited to a guy that you hang out with on a regular basis or work with and know quite well.