I figured I'd start a thread discussing a variety of gambesons and arming doublets/cottes. Feel free to share any thoughts or comparisons. There are a few pourpoints out there as well, but I haven't listed them here.
Here are a few I'm aware of:
Revival.us, 14th C. cotton gambeson:
http://www.revival.us/index.asp?PageAction=VIEWPROD&ProdID=83CAS/Hanwei GDFB gambeson:
http://casiberia.com/product_details.asp?id=AB0143Historic Enterprises arming doublet, 15th C:
http://www.historicenterprises.com/cart.php?m=product_detail&p=362&c=120Revival Clothing cotton gambeson:
http://www.revivalclothing.com/index.asp?PageAction=VIEWPROD&ProdID=11 (discontinued)
Revival Clothing Agincourt Arming cotte:
http://www.revivalclothing.com/index.asp?PageAction=VIEWPROD&ProdID=221Revival Clothing linen gambeson:
http://www.revivalclothing.com/index.asp?PageAction=VIEWPROD&ProdID=38This last one, the linen gambeson from Revival Clothing, is really very nice. I use it in my longsword classes, though I probably won't ever use it as my primary gambeson for my plate armor. I don't want to add grommets or points to it, or get it rapidly filthy as I tend to do with my armor. It's dry-clean only. I absolutely love it for use by itself, and I'm sure I'd be happy with a second one for my armor if I felt like spending the money.
Purpleheart Armoury (woodenswords.com) used to sell a cotton gambeson as well, and this is the one I currently use with my plate armor. It had the virtue of being machine washable and inexpensive, though I find that the sleeves pull up towards being like 3/4 sleeves when I clamp all the armor over it.