from http://social.technet.microsoft.com/wiki/contents/articles/12031.active-directory-powershell-ad-module-properties.aspx#Extended_Properties
"Most of the Get-AD* cmdlets support the -Properties parameter. If the
-Properties parameter is not included, only the default properties are
retrieved."

List of all properties:

Property 	Syntax 	R/RW 	lDAPDisplayName
============================================================================================
AccountExpirationDate 	DateTime 	RW 	accountExpires, converted to local time
AccountLockoutTime 	DateTime 	RW 	lockoutTime, converted to local time
AccountNotDelegated 	Boolean 	RW 	userAccountControl (bit mask 1048576)
AllowReversiblePasswordEncryption 	Boolean 	RW 	userAccountControl (bit mask 128)
BadLogonCount 	Int32 	R 	badPwdCount
CannotChangePassword 	Boolean 	RW 	nTSecurityDescriptor
CanonicalName 	String 	R 	canonicalName
Certificates 	ADCollection 	RW 	userCertificate
ChangePasswordAtLogon 	Boolean 	W 	If pwdLastSet = 0
City 	String 	RW 	l
CN 	String 	R 	cn
Company 	String 	RW 	company
Country 	String 	RW 	c (2 character abbreviation)
Created 	DateTime 	R 	whenCreated
Deleted 	Boolean 	R 	isDeleted
Department 	String 	RW 	department
Description 	String 	RW 	description
DisplayName 	String 	RW 	displayName
DistinguishedName 	String (DN) 	R 	distinguishedName
Division 	String 	RW 	division
DoesNotRequirePreAuth 	Boolean 	RW 	userAccountControl (bit mask 4194304)
EmailAddress 	String 	RW 	mail
EmployeeID 	String 	RW 	employeeID
EmployeeNumber 	String 	RW 	employeeNumber
Enabled 	Boolean 	RW 	userAccountControl (bit mask not 2)
Fax 	String 	RW 	facsimileTelephoneNumber
GivenName 	String 	RW 	givenName
HomeDirectory 	String 	RW 	homeDirectory
HomedirRequired 	Boolean 	RW 	userAccountControl (bit mask 8)
HomeDrive 	String 	RW 	homeDrive
HomePage 	String 	RW 	wWWHomePage
HomePhone 	String 	RW 	homePhone
Initials 	String 	RW 	initials
LastBadPasswordAttempt 	DateTime 	R 	badPasswordTime, converted to local time
LastKnownParent 	String (DN) 	R 	lastKnownParent
LastLogonDate 	DateTime 	R 	lastLogonTimeStamp, converted to local time
LockedOut 	Boolean 	RW 	msDS-User-Account-Control-Computed (bit mask 16)
LogonWorkstations 	String 	RW 	userWorkstations
Manager 	String (DN) 	RW 	manager
MemberOf 	ADCollection 	R 	memberOf
MNSLogonAccount 	Boolean 	RW 	userAccountControl (bit mask 131072)
MobilePhone 	String 	RW 	mobile
Modified 	DateTime 	R 	whenChanged
Name 	String 	R 	cn (Relative Distinguished Name)
ObjectCategory 	String 	R 	objectCategory
ObjectClass 	String 	R 	objectClass, most specific value
ObjectGUID 	Guid 	R 	objectGUID converted to string
Office 	String 	RW 	physicalDeliveryOfficeName
OfficePhone 	String 	RW 	telephoneNumber
Organization 	String 	RW 	o
OtherName 	String 	RW 	middleName
PasswordExpired 	Boolean 	RW 	msDS-User-Account-Control-Computed (bit mask 8388608)
PasswordLastSet 	DateTime 	RW 	pwdLastSet, local time
PasswordNeverExpires 	Boolean 	RW 	userAccountControl (bit mask 64)
PasswordNotRequired 	Boolean 	RW 	userAccountControl (bit mask 32)
POBox 	String 	RW 	postOfficeBox
PostalCode 	String 	RW 	postalCode
PrimaryGroup 	String 	R 	Group with primaryGroupToken
ProfilePath 	String 	RW 	profilePath
ProtectedFromAccidentalDeletion 	Boolean 	RW 	nTSecurityDescriptor
SamAccountName 	String 	RW 	sAMAccountName
ScriptPath 	String 	RW 	scriptPath
ServicePrincipalNames 	ADCollection 	RW 	servicePrincipalName
SID 	Sid 	R 	objectSID converted to string
SIDHistory 	ADCollection 	R 	sIDHistory
SmartcardLogonRequired 	Boolean 	RW 	userAccountControl (bit mask 262144)
State 	String 	RW 	st
StreetAddress 	String 	RW 	streetAddress
Surname 	String 	RW 	sn
Title 	String 	RW 	title
TrustedForDelegation 	Boolean 	RW 	userAccountControl (bit mask 524288)
TrustedToAuthForDelegation 	Boolean 	RW 	userAccountControl (bit mask 16777216)
UseDESKeyOnly 	Boolean 	RW 	userAccountControl (bit mask 2097152)
UserPrincipalName 	String 	RW 	userPrincipalName

For more docs on the complete list of properties, see:
http://social.technet.microsoft.com/wiki/contents/articles/12037.active-directory-get-aduser-default-and-extended-properties.aspx