We did a Race Car Birthday last year for my son's 5th birthday and went with the black and white checkered flag theme with red accents. I got the B/W Checkered pennants strung together at Oriental Trading online. Also, we got the checkered paper plates etc. at US Toy in Overland Park KS, they are online too. They had a plastic banner that said "Welcome Race Fans" that was B/W with Red print. I used cheap red plastic table cloths and red plastic cups and then had the B/W checkered plates.
For the cake, I did 9x13 cake frosted white and put Hotwheels around the edges as a border used a decorating bag/tips to write Happy Birthday.
As for games, we made "race cars" out of boxes for the kids to step into and race around. I got cardboard file storage boxes, cut out the bottoms, spray painted them in red, black, silver, and white. Decorated them with numbers on the side, covered cardboard circles with foil for head lights that was it. The kids stepped into the box, used the handles that were already in the file storage box and ran around with the box around their waist as if they were race cars. They LOVED it and we did little relay races etc. and everyone had so much fun just taking turns running around in the "cars". Have fun and let me know if you want to see pictures of our party.