Our favorites are the Backstage Magic (takes all day and visits all parks)
Segway tours (we have done both and like both with slight preference to FW)
Garden's of the World, and for a quick little inexpensive one, try "behind the seeds" at the land pavillion. There are discounts on all of them.
If you are staying CL at AKV, the best is Sunrise Safari!!! We also really enjoyed the Wanyama sunset safari at AKL, but it is a bit pricey and includes dinner at Jiko.