For super-high value, MarkMonitor is about the only game in town. Unlike most others, MarkMonitor offers domain locking at the
registry level, for registries that offer it (VeriSign does for .com and .net), in addition to other, often personalized, security features. See example below of registry-locking in acton - note my emphasis in bold:
Domain Name: GOOGLE.COM
Registrar: MARKMONITOR INC.
Whois Server: whois.markmonitor.com
Referral URL:
http://www.markmonitor.com
Name Server: NS1.GOOGLE.COM
Name Server: NS2.GOOGLE.COM
Name Server: NS3.GOOGLE.COM
Name Server: NS4.GOOGLE.COM
Status: clientDeleteProhibited
Status: clientTransferProhibited
Status: clientUpdateProhibited
Status: serverDeleteProhibited
Status: serverTransferProhibited
Status: serverUpdateProhibited
Updated Date: 20-jul-2011
Creation Date: 15-sep-1997
Expiration Date: 14-sep-2020
Many of the big name registrars say they offer iron-clad security, but don't really. Ie. GoDaddy's Executive Lock is mostly more market speak, while code generators, such as NameSafe, are great in theory, but how secure are they really, especially when often being offered in bulk to customers for little to no extra cost.
Don't get me wrong, GoDaddy, eNom (dealing direct; not through reseller), and Fabulous are all very good compared to most, but their security pales in comparison to what MarkMonitor offers...
Not saying MarkMonitor is ideal for domainers due to the high cost of their services, but point them out to illustrate there's a level of security above and beyond what most domainers are aware of.
Ron