I want to run a 60 amp panel in my garage off my 100 amp panel in my house. What size copper wire should be used on a 150 ft. run. Buried in plastic conduit? Also, I can only find 60 amp panels with 2 or 4 breakers. Do they make them bigger? I think I will Need six for sure!

What amp breakers do you plan to install? I normally recommend that several be 20 amp for a garage. Is there some reason you do not want to start with a larger panel. Over time I keep adding more and more stuff to my garage so a larger panel may be a better fit for you. I think #6 would be OK for what you describe but TK will stop by and give you better advice. This 60 amp box can support 8 circuits http://www.lowes.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10151&catalogId=10051&cId=SEARCH&productId=3128391&cm_mmc=SCE_gps-_-gps-_-gps-_-Square%20D%2060-Amp%204-Space%208-Circuit%20Generator%20Panel%20QO48M60DSGP

Ballenger is correct, #6 copper wire with THHN/THWN insulation will be fine.

You will need three # 6 for the two live and one neutral, and a #10 green for the equipment ground.

Be sure to install an equipment ground bar in the new panel, and do not connect the neutral to the metal box of the panel.

Keep in mind, all 120 volt receptacles in a garage need to be GFI protected.

TK,
If this was a couple of 240 volt circuits, would you have reduced the Neutral? Or just to be safe and if all fails, And/or, it will reduse Voltage Drop?

I do not consider reducing neutrals for such a small feeder.

Reduce voltage drop?

"I do not consider reducing neutrals for such a small feeder."
That's what I was Looking for.

As far as Voltage drop, I was grasping. It would reduce voltage drop, however slight.