I will have to agree with the dinner option. (Although, keep in mind the preferences of the mommy & daddy!! Make it something easy or that you know they will like.) If you're coming to meet the baby, it's nice to bring a snack with you for everyone to enjoy - that way the new mommy doesn't have to worry about what to make to 'entertain'. (I know, no one expects her to.....but still.) A fruit tray, veggie tray, cold cuts, cheese & crackers are all things she can use to share with other guests that stop in by simply putting it on a smaller plate or tray...not to mention having it around to snack on themselves.
A basket with easy snacks or easy to make things: microwave popcorn, Tastefully Simple beer bread/dips, fruit, muffins or bagels, soup, etc.
I also like the idea of a gift certificate so the new dad can either pick up carry out or the parents can get out of the house for dinner!
Another thing that is helpful....ask the parents if they are ready for visitors, and ask what time works best for them. Don't just pop by - and try to give them a day or two's notice.
If you're on your way over, call before you leave and ask if there's something they need from the grocery store or something they want (Slurpee craving, etc?!). It's much appreciated to not have to run out later and a nice gesture!!