If you want to buy a gift-diapers, in size 1 and size 2 (everyone buys hte small one, babies grow unbelievably fast), wipes (never enough), a gift certificate to get mommy's hair done or a massage...
I don't advise baby clothes-because everyone gets new babies clothes and many of them end up donated having never been worn, because the babies grow so fast.
If you want to be helpful-a gift basket of pre-made meals, fresh fruit and veggies....
And for sure like Neon said-offer to clean can be HUGE-sometimes giving someone a gift certificate for cleaning services-with specified things, like bathroom cleaning, kitchen cleaning, vacuuming etc is less invasive to them than just saying "would you like me to come clean?".
Even if it's for YOUR services-it feels a bit less invasive.
"Love As Thou Wilt"