Whether you buy domain names on a large scale or not, this service may be of interest: Ofindo is a (relatively) new website where you can compare registrars offers.
Using different criteria (TLD, registrar's country, currency and/or mean of payment), users may select which registrar best suits their needs. Comparison is only possible among the providers which registered and publish their offers.
Users who also search for additional services, such as hosting, or parking, can also gather this information when comparing. But it is not possible to compare the prices or features of those services.
It is not possible, neither, to know what is the language of the registration agreement. The lawyer is speaking: Such an information is useful as, for TLDs for which UDRP rules apply, the language of the procedure is the language of the registration agreement!
The launch of this website is another clue of the growth of the domain market.