My youngest son loved balls (it was his first word, it was all he played with) so it was easy to come up with a ball birthday party for his 1st. This was a large party (all our family & friends were invited, as with all our 1st birthday parties).
The Decorations: I found every ball I could... I bought a bag of play balls (the ones that go in ball pits) at Toys R Us and filled a clear bucket for the centerpiece. Then basically put balls wherever I could. I got kick ball- size playground balls at the dollar store that doubled as decorations and favors (this was a huge party...my husband's family is very large...there were a lot of balls around).
I found the "paper lanterns" at a party store, they actually had graduation caps hanging off of them (which I cut off) and no colorful ribbons to hang them from (which I added), don't be afraid to alter something to make it work for you. His banner was just letters I printed out on the computer, cut out, matted with colorful paper, and strung together with paper ribbon.
The Cake:This cake I actually didn't bake, just decorated. I ordered a pre-made cake from Sam's Club, and had them just frost it white, smooth, with no borders (I think they thought I was a little crazy). This made it really easy to just add the bouncing balls and dash marks (thanks to Martha Stewart for this design) and it tasted great.
The Menu:
We don't do meals for big parties, so we plan it for mid-afternoon and serve snacks. This party was very laid back.
Veggies & Dip
Cowboy Caviar & Tortilla Chips
Lil' Smokies in a blanket & Barbecue Sauce
Fruit & Cream Cheese Dip
Ice Cream & Cake

I was inspired by these baseball Easter eggs that I found on clearance. I "signed an autograph" of the kids' name on each & filled them with candy, these doubled as place markers and favors.
For the table I made pennants out of stiff felt. First I cut elongated triangles out of the felt, used ribbon to trim one edge and make ties. Next I printed out Happy 5th Birthday, Play Ball, and Home Run in "Team Spirit" font in appropriate sizes on the computer, and traced the words onto the felt; use a light box (or your window), then I colored them in with markers. I tied them to dowels and stuck them in a bucket of sand...super easy!
The Cake:

