Friends , I want to know  the best reseller hosting providers. My budget is $20 Monthly. Minimum 50GB space. 24*7 support . Free billing manager and free domain reselling
I would suggest you to buy whmcs license then buy reseller hosting. It will save you a lot of cost in long run.
What is the point in buying WHMCS without a reseller account, I don't see the point in your post since it's pointless unless you are referring to Owned license.
Go for HostGator. They will provide you all that for free, but you will have to step up your budget by over $5.
Try GearServe, the Professional Plan gives you 60 GB Storage, 1 TB bandwidth ! You can use BoxBilling as a billing manager (Its free). gearserve.net/pricingr.html
Go for host department as they are providing it at very cheap rates and they also meet ur requirements.
From the personal experience I recommend you Interactiveonline.com reseller plans, they are providing stable and fast response support.