Congratulations! We bought our son's BM some comfy PJ's and slippers. She is also an avid reader, so we included some books. We also took a picture of the BM, BF, my husband and I a few weeks before our son was born. We had the picture framed and gave them that also. I also love the idea of a bracelet or necklace with the baby's birthstone. But, I would advise to buy/give that until after the paperwork has been signed. We were 99.9% positive that our adoption was a sure thing, but we still had to be cautious. This site also has some cute ideas:
http://www.heartonyourwrist.com/index.php
When we first bet the BM and BF, we gave them a gift from the Ghiradelli Outlet in San Leandro. It was a cable car filled with little chocolates. They loved it! What about something like that for their daughter?
Does the BF like sports? What about something to do with the Giants? No matter where they live, he will think of you guys when he sees/wears the Giants item.
I also can't believe that someone would consider a gift for them 'weird.' As an adoptive parent, I can't imagine not helping them out a bit and giving them small tokens to thank them for making my husband and I parents. If not for them, we would not be parents. The gave us the gift of a child and the gift of parenthood.
Best of luck! :)