Just some ideas (as you can see from my user name I have a little experience in this)
Memory box for each baby. Make sure they're fairly good size. You may not have time to fill in a baby book right away (I'm planning on starting mine when the twins are in kindergarten). You can put items that wouldn't fit in an album and throw in dated pieces of paper with milestones on them. Later, when you have more time, you can go through the pieces of paper and write them in the book (gifts, first smile, first step...)
As much maid service as you can afford for the first month(s) of your babies lives.
gift certificates for your wifes favorite restaurants that do takeout (Olive Garden, Boston Market, Chili's, Outback...)
If your wife isn't on bedrest arrange to take her out for a grown-up date before the children are born. If she is on bedrest make a nice candlelit dinner that she can eat while lying on her side on the couch.
Jewelry is always nice. DH gave me diamong earrings the day the twins were born. I wear them every day. Another option would be a locket that holds two photos.
I wish you all the luck and congratulations in the world. Twins truly are a blessing.