Sure, there are some people who might have a problem with your registering with Planned Parenthood of Maryland and donating money to provide health services to women in need, especially in desperate economic times. But if you are like me, and are the type of person that openly and fully supports the mission of Planned Parenthood (I spent 1.5 years at NARAL and have started to volunteer for PPMD since moving to Baltimore), you might choose to forego other people's opinions.
To suggest donations to PPMD, you could put a link to their website - or you could add suggested donation amounts, to make it clear that Planned Parenthood does more than just abortion. For example: "$25 will distribute 100 condoms this year" or "$50 will provide a woman in need with a PAP smear" or "$100 will help vaccinate a teenager with no insurance against cervical cancer".
I can't come up with cute favor ideas relating to this, except condoms if you're having an adults only reception, and even I will hesitate to donate in my guest's honor to PPMD - because I believe in choice, and I believe in choosing not to support service providers if you don't want to. I would be extremely upset if I attended a wedding that chose to give money to a Crisis Pregnancy Center or to an anti-choice organization on my behalf. If you do choose to give a donation-as-favors, you could consider making two donations - one to PP and one to a less controversial charity, and making two piles of cards and letting your guests "choose" which card is the donation they want made on their behalf.
If you have a local or national charity which you would like for me to mention in this series, please leave a comment and a link to tell me more about it!