I'm currently pregnant with my 2nd, so, based on experience:
- If you want to get baby clothes, get 9mo+. EVERYONE buys cute little outfits in tiny sizes, so you wind up with like 15 0-3mo PJs that the kid wears 3 times and grows out of.
- Kids get a LOT of recieving blankets and stuffed animals; most never get used. However, if you can find like 12 flat cloth diapers (big squares of super-absorbant material), include those with a note about how they're for 'baby messes'. Put them down before the baby, wipe up puke, wipe up food, wipe down guests... we basically had 2-3 in every room and washed them every 2 days. Most used bits of cloth ever. :) We've included that in shower gifts since. Parents will universally look at them weird, and within a few months of the kid being born I'll get a text along the lines of 'these things are amazing and so useful'.
- BOOKS. Cardboard books. Or those fabric ones the kid can chew and can't rip. (I highly recommend anything by Robert Munsch, ESPECIALLY The Paperbag Princess and Mortimer.)
- Anything handmade.
And thing 1 friend did and I appreciated it SO MUCH: everyone brings food to new parents, which is awesome and appreciated. But everyone brought muffins and casseroles. When, 2 weeks in, a friend showed up with a huge salad and a flat of berries, I felt like angels started singing. :) If you live close enough that that's an option once the baby is born, seriously: fresh foods. :)