A full listing of all DNS Records can be found on Wikipedia:
http://en.wikipedia.org/wiki/List_of_DNS_record_types
MX:
Mail exchange record
Maps a domain name to a list of message transfer agents for that domain
NS:
Name server record
Delegates a DNS zone to use the given authoritative name servers
TXT:
Text record
Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework, DKIM, DMARC, DNS-SD, etc.
SRV:
Service locator
Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.
Name server record
Delegates a DNS zone to use the given authoritative name servers
TXT:
Text record
Originally for arbitrary human-readable text in a DNS record. Since the early 1990s, however, this record more often carries machine-readable data, such as specified by RFC 1464, opportunistic encryption, Sender Policy Framework, DKIM, DMARC, DNS-SD, etc.
SRV:
Service locator
Generalized service location record, used for newer protocols instead of creating protocol-specific records such as MX.
