I gave my DDiL a voucher for a Spa day at a lovely hotel, with afternoon tea for her and DS. The voucher was valid for six months after DGS's due date. I included a home made gift token, stating that I would baby sit on whichever day they chose!
We had also given her a course of reflexology appointments, for before the babe was born, but you might be cutting that a bit fine now time wise! She did say the reflexology was the most relaxing thing she'd ever experienced though!
Our DDiL found her hands got very dry, so perhaps a lovely fragranced hand cream as a little treat!