There are two handy websites online which helps quite extensively in tracking problems with domain name records and DNS incosistencies.
I used them today to learn more about a problem with a non-resolving DNS though it has already a record in a properly configured Bind nameserver possessing a proper PTR record. Here are three handy online DNS checkers:
1. Squish.Net/DNSCheck – contains Tons of useful debugging information related to the possible problem
2. DNSCheck.iis.se – provides with less information, though still really handy
Some more handy information realted to DNS can be obtained via R. Scott’s DNS Oversimplified
3. TheDNSReport – provides good and extensive info on problems