I am having a hell of a time finding a stainless steel cup that fits around a 1L and .5L nalgene bottle.  I lost the only bookmark that I had for them.
Anybody point me in the right direction for one?

If anybody else is looking for one, here it is:
www.practicaltactical.net/prostores/servlet/-strse-237/MSR-Stainless-Steel-Nalgene/Detail

I hear all the cool kids use titanium.

Yeah, I know.  But I never got into the whole Gucci-gear stuff.  
I looked at some of the Ti cups, but they just felt too light.  They might hold up to being beat on and trashed from heavy constant use, but I know the steel cups will.
I've got an old stainless sierra cup that I bought when I took a summer biology class that was two months in the mountains of Colorado.  The wire handle is a little bent, but it is still fully functional and took a tremendous beating.
I may try the Ti cup one day.

For Ti cookware, try Snowpeak products.

A 1L Nalgene, with a SnoPeak Titanium 700 cup fit over the bottom and an MSR 600ml SS cup over the top will all fit in a Kifaru LiterPlus Pouch - and no rattles.