NOT two of things the same and especially not two soft toys of any description.
My best buys/gifts so far:
Socks that stay on (only BabyGap will do - not the ones that roll/fold over at the top)
A mobile for the changing table (with twice as many nappies to change, if they can be fuss free changes so much the better. I recommend the 'FlutterBug' by Infantino. I just bought this for a friend who had twins and she said it was the most useful gift she had received. You could also send a changing mat with instructions that she must have a changing station both upstairs and down - essential with twins.
I have also had enormous mileage out of my babygym as you can put one baby underneath while you tend to the other. Ditto good mobile for the cot - something really fascinating like the TinyLove one, not twee lullaby player.
I've got two suggestions - one to help them sleep one to keep them awake!
a prince lionheart slumberbear (http://www.amazon.co.uk/Prince-Lionheart-Slumber-Bear-Plus/dp/B000L3ISWI). It plays womb sounds and if they start using it early enough (within a few weeks of birth) will lull them back to sleep when they cry. Our twins still have theirs 5 months later and it definitely soothes them. Failing that a tinylove mobile (http://www.amazon.co.uk/Tiny-Love-Symphony-in-Motion-Mobile/dp/B000MDSEPS)- plays music and spins toys above their heads and keeps them entertained in their cot when you need to do stuff.
both have been invaluable and if I hadn't bought them both for myself I'd have thought the giver my best friend forever!
Loved the box of Trumpette socks that was given to our DTs. Lovely, fun and colourful also the only socks that didn't come off and lasted forever. Why, the boys were wearing them still around their first birthday.