TLD List - Compare Prices of All Top-Level Domains
Domcomp - No-nonsense domain price comparisons, updated daily
Tldes - Comparison of domain prices of 86 registrars. Data is updated every 4 hours.
Pricepeek - Compare prices of the same product across all Amazon locales
The Mac Index - Compare Apple product prices in different countries
NameSilo - Domain registration. That's it! And that's what makes it special.