SIG : Signature (RFC 2535)
Signature record used in SIG(0) (RFC 2931). Until RFC 3755 was published, the SIG record was part of DNSSEC; now RRSIG is used for that.

NS : name server record (RFC 1035)
Delegates a DNS zone to use the given authoritative name servers

NSEC3PARAM : NSEC3 parameters (RFC 5155)
Parameter record for use with NSEC3

CERT : Certificate record (RFC 4398)
Stores PKIX, SPKI, PGP, etc.

DNSKEY : DNS Key record (RFC 4034)
The key record used in DNSSEC. Uses the same format as the KEY record.

OPT : Option (RFC 2671)
This is a 'pseudo DNS record type' needed to support EDNS

IPSECKEY : IPSEC Key (RFC 4025)
Key record that can be used with IPSEC

PTR : pointer record (RFC 1035)
Pointer to a canonical name. Unlike a CNAME, DNS processing does NOT proceed, just the name is returned. The most common use is for implementing reverse DNS lookups, but other uses include such things as DNS-SD.

RRSIG : DNSSEC signature (RFC 4034)
Signature for a DNSSEC-secured record set. Uses the same format as the SIG record.

MX : mail exchange record (RFC 1035)
Maps a domain name to a list of mail exchange servers for that domain

AFSDB : AFS database record (RFC 1183)
Location of database servers of an AFS cell. This record is commonly used by AFS clients to contact AFS cells outside their local domain. A subtype of this record is used by the obsolete DCE/DFS file system.

DLV : DNSSEC Lookaside Validation record (RFC 4431)
For publishing DNSSEC trust anchors outside of the DNS delegation chain. Uses the same format as the DS record. RFC 5074 describes a way of using these records.

TKEY : Transaction Key (RFC 2930)
One way of providing a key to be used with TSIG

SPF : SPF record (RFC 4408)
Specified as part of the SPF protocol, as an alternative to storing SPF data in TXT records. Uses the same format as the TXT record.

A : address record (RFC 1035)
Returns a 32-bit IPv4 address, most commonly used to map hostnames to an IP address of the host, but also used for DNSBLs, storing subnet masks in RFC 1101, etc.

NSEC : Next-Secure record (RFC 4034)
Part of DNSSEC—used to prove a name does not exist. Uses the same format as the (obsolete) NXT record.

DHCID : DHCP identifier (RFC 4701)
Used in conjunction with the FQDN option to DHCP

NSEC3 : NSEC record version 3 (RFC 5155)
An extension to DNSSEC that allows proof of nonexistence for a name without permitting zonewalking