Finding a Safari company via the internet, and trusting them enough to wire them money before you ever show up in Nairobi is not an easy thing to do. I want to give a plug to Aramati Safaris and the owner, John Ndegwa.
I've used Aramati two times now for the logistical needs of me and my college students. I know several other proffs and NGO's who use Aramati as well.
Both times, the service was excellent. We were met at the airport, brought around the country (including on Safari) in safe, reliable vehicles with very knowledgeable and competent drivers. John is always ready to go the extra mile to make sure all your needs are met and actively seeks to make sure things are done right.
I don't work for Aramati. I'm just giving them a plug in case you need a reputable company to help you with your next East Africa trip.
Their website is: http://www.aramatisafaris.co.ke