The best gift ideas come from the heart, and are about something he loves or a memory you share. Try taking him for a night out at his favorite restaurant, on you.
I know one perfect gift for dads. It's my dad's birthday recently and I've been thinking for a long time about what to buy him. I found a site called CaricatureMaster and decided to order golf caricature of him because he is an passionate golfer. They did a fantastic job, my dad was thrilled, he said it was the most unique gift he ever received.
There are several specialized online retailers that have a very unique collection of gifts, not only for Christmas but in general. Some of these suggestions are Uncommongoods and Iwantoneofthose.
woodlandandtrustshop.com/dedicated This site will be perfect. This is because they do custom flowers for any occasions. Cheap and is affordable. I'm sure your dad will love it.
Dad's want something that benefits the baby and shows that he cares about he/she. The best gift would be to get a shirt/outfit that says something about dad or daddies something.
A unique gift would be something your father would really enjoy. Since he is retiring, are there any hobbies he may like to spend time doing such as golf, or wood working. Buying something for your Dad that he would enjoy doing would be money well spent.
Some good ideas you could use are gift-cards as they are like giving him money, but more professionally. If you know what your dad likes, like gaming for instance, then giving him a game card would be brilliant, if however you don't know, you can just give him an amazon or eBay gift card so he can decide what he wants.
If you go to www.gifts.com/ideas/him you can find many gift ideas for a new dad. Another place to look is on ebay.com There you just enter dad gifts and many ideas will pop up with price too.
Since the new dad will probably have a lot of things to think about, try to find a gift that will be useful and will help him in everyday life, like a baby carrier.
It depends on his interests. Some good ideas are a Leatherman pocket tool if he likes the out-doors or gadgets, a good bottle of wine if he drinks alcohol or an electronic gadget or tool (dad can never have enough power tools).
For men, some of my go to gift ideas are perfume (preferably in a set), a nice pair of shoes, a robe, slippers, hats, or anything custom maid. It is elegant and shows that you care.
It might be better to send your dad on a unique experience or plan a day with him. You can take him out to the ballgame or send him on a WWII Fighter plane ride.
Maybe you could get him an actual amazon.com gift card or a Wal-Mart gift card. That's what my brother usually gets my dad and he's often proud of it.