Can some one point me to the right direction which company's i have to look at and what is the preferred way of doing your billing if your a reseller.

Thanks

There have been many discussions about this on these boards. Try going here and doing a search: http://www.webhostingtalk.com/search.php?s=

If you could refine your question, it would help a lot! Are you wondering about the billing cycle (ie pro-rating, etc) or are you wondering how to physically bill them?