I agree that NameSilo is the best option for bulk domain purchasing - especially if WHOIS privacy will be used. They have the best rates I have seen via their Discount Program (http://www.namesilo.com/Support/Discount-Program) and WHOIS privacy is free always, unlike many companies like Name Cheap that charge a few dollars for each domains for WHOIS privacy after the first year.
We could say, are you promoting this site in particular? I mean, the question is about bulk domain registration but this site offers everything except domain registration, hence such recommendation is worthless for this purpose.
I would suggest, HioxIndia. It is the 8years old experience company and provides cheapest and secure domain names for those who are looking trustworthy services and reliable solutions.
I recommend you to use domain registration provided by Eurodns.com. They are delivering reasonable deals with attractive offers and helpful support.