I like the bouncy seats too! But if you have to buy 4 of them, you're looking at at least $100-$150 you will be spending. And the ocean aquariums are great as well.
For something less pricey, I love the Carters sleeper gowns...the ones that just have elastic gathering at the bottom vs. legs. A lifesaver for middle of the night diaper changes- no zippers, snaps, etc...just lift it up! And they are so soft! I think they're usually about $16 for a two pack.
And might I add, that for my first son, a LOT of people loved the idea of giving me bundles of shampoo/baby wash/powder/desitin/ towels....I swear to God I didn't have to buy any of that stuff til he was nearly 2 or 3!!!!!!!! I generally don't give that as a gift as I remember how much I got!