What should I wear under my cycling helmet?

[TheBreeze]

Hey guys.  I am an avid triathlete and cycle year round (I live in the NYC area, brrr).  I am going sly in just a few weeks and would appreciate suggestions on what to wear underneath my helmet both in the summer and winter, to protect the dome and help keep me at the right temperature.   

I am a fan of the De Soto products and saw this item that might be good for the summer.  http://www.desotosport.com/products/product.asp?Category=accessories&ProdID=SHB

You guys just wear a skull cap underneath in the winter?

Thanks! 

[D.A.L.U.I.]

That looks very much like the Under Armor skull cap.  I've got one to wear under safety helmets--particularly to keep the dirt and other stuff that might be on loaned equipment like that.  I'll also be using one under my motorbike helmet so I don't have to constantly wash the removable liner--sunscreen probably gunks those up too. 
During the winter, or what passes for it down here in NO, I have a fleece beanie--and that sucker is always with me when I have to go to the home office in upstate NY between October-March!  Damn, it gets cold up north!

[Jack21]

http://www.pricepoint.com/detail/14404-510_GATHN5-1-clothing-6-Head-Wear/Gator-Hot-Noggen-Neoprene-Helmet-Liner.htm

Used to wear this under my helmet in the winter. You might have to adjust the size of your helmet.

[TheBreeze]

Thanks guys, that helps. 

I grew up in Upstate NY and where I live now (NYC Metro) is like the tropics by comparison!

Jack, thanks for that, it's pretty much exactly what I was looking for.