I bought this blow up at Walmart a few years back for $6. I also found a Scooby Doo blow up that I used last year for less than $10. This stays beside the birthday child's desk for the day. They also receive a certificate and a bookmark. I found these cute visors for like 50 cents for a pack of 12 on clearance at Michael's. All the students sign the hat with a birthday wish.
For summer birthdays, I celebrate their half birthday. Having a summer birthday myself, I understood the importance for each student to have their own day and not be clustered as a group at the end of the year. I'm very careful to write the 1/2 birthday dates on my calendar. I think parents appreciate it as well, because they're not pressured to bring in goodies for their child, in addition to all the other demands that the end of the year brings. The kids love this and they all want to know when their half birthday is!