Below you find an overview of the most used DNS records. Please note that not all records are usable in each package.
Faulty entries in the DNS can lead to inaccessibility.

RecordType:          A
Description:        IPv4 address of a host
Standards for target: must contain IP adresses only (IPv6) (IPv4)
Example for target:    88.88.99.22
Wikipedia link:       http://en.wikipedia.org/wiki/List_of_DNS_record_types

RecordType:          AAAA
Description:        IPv6 address of a host
Standards for target: must contain IP adresses only (IPv6)
Example for target:    3efe:8124:3000:bf0::1

RecordType:         AFSDB
Description:       Resource Record for Cell Database server of the Andrew File Systems
Standards for target: #subtype hostname (where subtype has to be a number)

RecordType:             CERT
Description:           Resource Record for saving certificates (RFC4398)
Standards for target:    (see RFC 4398)
Further links:    http://tools.ietf.org/html/rfc4398

RecordType:          CNAME
Description:        definies an alias name for an existing DNS name
Standards for target:  Always must be a hostname (FQDN)
Example for target:    subdomain.domain.tld
Wikipedia link:       http://en.wikipedia.org/wiki/CNAME

RecordType:         DNSKEY
Description:       contains  a public key (DNSSEC) assigned to the name

Standards for target: ---
Wikipedia-Link:     http://en.wikipedia.org/wiki/DNSKEY

RecordType:         DS
Description:       handles the linkage of DNSSEC signed zones (DNSSEC)
standards for target: ---

RecordType:         HINFO
Description:       Hardware Info Record
Standards for target: text containing the used hardware for instance
Example for target:   i686 Linux

RecordType:         KEY
Description:      contains a public key assigned to the name
Standards for target: see RFC 2535
Wikipedia link:     http://en.wikipedia.org/wiki/List_of_DNS_record_types

RecordType:         LOC
Description:       location / see RFC 1876
Standards for target:   51 51 0.123 N 5 52 0.000 E 4.00m 1.00m 10000.00m 10.00m
Wikipedia link:     http://en.wikipedia.org/wiki/List_of_DNS_record_types

RecordType:         MX
Description:       mail exchange –  the mail server competent for the domain
Standards for target: hostname (no IP), use prio field for priority
Example for target:   mx10.domain.tld
Wikipedia-Link:      http://en.wikipedia.org/wiki/MX_record

RecordType:         NAPTR
Description:       Naming Authority Pointer - expansion of the A Resource Record
Standards for target: entries in the order: order, preference, flags, service,
                              regex, replacement
Example for target:    '110  30  "s"  "z3950+I2L+I2C"     ""  _z3250._tcp.domain.tld'.
Wikipedia-Link:      http://en.wikipedia.org/wiki/NAPTR

RecordType:         NS
Description:       hostname of an authoritative name server
Standards for target: hostname (FQDN), no IP
Example for target:   ns1.domain.tld
Wikipedia-Link:     http://en.wikipedia.org/wiki/NS_record

RecordType:         NSEC
Description:       NSEC DNSSEC record type (DNSSEC)
Standards for target: ---
Wikipedia link:     http://en.wikipedia.org/wiki/List_of_DNS_record_types

RecordType:         PTR
Description:       Domain Name Pointer (for Reverse Mapping, assigning names to IP addresses)
Standards for target: ---
Wikipedia link:     http://en.wikipedia.org/wiki/PTR_record

RecordType:         RP
Description:        responsible person (RFC 1183)
Standards for target: ---  
Example for target:   tim.domain.tld tim.people.domain.tld
                             Means that tim@domain.tld ist responsible and more information can be found in the TXT record   "tim.people.domain.tld"

Wikipedia-Link:     http://en.wikipedia.org/wiki/List_of_DNS_record_types
               
RecordType:         RRSIG
Description:       contains a digital signature (DNSSEC)
Standards for target: ---
Wikipedia link:     http://en.wikipedia.org/wiki/RRSIG

RecordType:         SPF
Description:       Sender Policy Framework
Standards for target:  see www.openspf.org
Wikipedia link:        http://en.wikipedia.org/wiki/List_of_DNS_record_types
Wichtig:               input in the customer center must be enclosed in inverted commas, e.g.,
                             "v=spf1 ip4:85.31.185.13 a mx ~all"

RecordType:           SSHFP        
Description:         for Secure Shell (SSH) fingerprints
Standards for target:  an example from RFC 4255:
                               '2 1 123456789abcdef67890123456789abcdef67890'

RecordType:          SRV
Description:       offered service
Standards for target:  priority is set in the prio field, the rest in the target field
Example for target:    100 389 mars.conaxis.ch
Wikipedia-Link:       http://en.wikipedia.org/wiki/SRV_record

RecordType:          TXT        
Description:        loosely definiable, also used for Sender Policy
                              Framework (SPF)
Standards for target:  ---
Wikipedia link:      http://en.wikipedia.org/wiki/TXT_record
Important:               the entries must not be enclosed in inverted commas

Additional links:
Resource records at Wikipedia
DNS system at wikipedia