J.W.
Hello D.,
Being from Holland myself I was also new to the baby shower phenomena. Key is to have your gift with you at the shower, because the gifts are unwrapped during the party (so take that into account when you order from the registry).
Whether it's good form here or not, I tend to like to get something for the mom, as so many gifts are for the baby already. Expect to spend at least $35 - up to $75 (or $100!) depending on how close you are to the person [American moms, please verify this].
Gift that I found most useful were: swaddle blanket, bibs (the really good thick ones), stroller blanket, bundleme (for in infant car seat) or the Sleep Sheep (makes soothing sounds). For the moms, I loved the Bella Materna nursing wear. If you rather not pick for her, they do have gift certificates online, and the website has the largest variety --although I only know of Village Maternity selling that brand in retail, U-Village. If you are a Seattle local, there's a fancy baby store with (expectedly overpriced) designer baby gear that's excellent for gifts: Tottini behind the REI on Yale.
Good luck shopping!
J