In general usage, member template variables begin with {MEMBER. Sometimes however you may be within the scope of some other member yet want to use a variable which is for the person viewing the page. To accomplish this, use {THISMEMBER instead of {MEMBER. The {THIS prefix tells the script that you mean the viewer of the page, not the member whose profile or article we may be dealing with.

{MEMBERADMIN} - If viewer can edit this profile, contains the html for the article to do it, otherwise blank.
{MEMBERISADMIN} - Returns 1 (true) if member is an administrator, 0 (false) otherwise.
{MEMBERAVATAR} - The member's avatar.
{MEMBERHASSIG} - Returns 1 (true) if member has a signature, 0 (false) otherwise. {MEMBERALLOWUSEREMAIL} - Returns 1 (true) if member allows emails from other users, 0 (false) otherwise.
{MEMBERALLOWEMAIL} - Returns 1 (true) if member allows emails from administrators, 0 (false) otherwise.
{MEMBERREGDATE} - Date that the member registered.
{MEMBERISGUEST} - Returns 1 (true) if member is an unregistered guest, 0 (false) otherwise.
{MEMBERISREGISTERED} - Returns 1 (true) if member is a registered member, 0 (false) otherwise.
{MEMBERID} - The id number of the member.
{MEMBERNAME} - The username of the member.
{MEMBERSAFENAME} - If emails are being used as names, this will hide the domain name part of the name to protect from spammers.
{MEMBERSUBMISSIONS} - Number of articles the member has submitted. This is script-neutral, so when used in a different WSN script it shows the appropriate value... useful if you share templates amongst the scripts.
{MEMBERPOSTCOUNT} - Number of comments the member has submitted. This is script-neutral, so when used in a different WSN script it shows the appropriate value... useful if you share templates amongst the scripts.
{MEMBERLINKS} - Number of links the member has submitted for WSN Links.
{MEMBERARTICLES} - Number of articles the member has submitted for WSN KB.
{MEMBERIMAGES} - Number of images the member has submitted for WSN Gallery.
{MEMBERTOPICS} - Number of topics the member has submitted for WSN Forum.
{MEMBERITEMS} - Number of items the member has submitted for WSN Classifieds.
{MEMBERCOMMENTS} - Number of comments the member has submitted for Links, Gallery, KB, Classifieds.
{MEMBERPOSTS} - Number of posts submitted for WSN Forum.
{MEMBERUSERGROUP} - The number of the member's usergroup.
{MEMBERPASSWORD} - DO NOT USE THIS, as it is the md5 hashed version of their password rather than their actual password.
{MEMBERIP} - The IP address of the member.
{MEMBERTOTALHITS} - Total hits out of sites submitted by this member.
{MEMBERTOTALHITSIN} - Total hits in of articles submitted by this member.
{MEMBEREMAIL} - Email address of this member.
{MEMBEREMAILDISGUISE} - Email address of the member disguised from spam spiders by using the form person at domain dot com.
{MEMBERTEMPLATE} - Template set this member is using.
{MEMBERLANGUAGE} - Language this member is using.
{MEMBERSIGNATURE} - Member's signature.
{MEMBERAVATARNAME} - Name of avatar file on disk.
{MEMBERSTYLESHEET} - Member's selected style.
{MEMBERALBUMID} - Id number of member's personal link list.
{MEMBERFAILEDATTEMPTS} - Number of times in the last day that someone has attempted and failed to login to this member's account.
{MEMBERCOMMENTAPPROVAL} - The ratio of approvals out of total voters for comments posted by this member. Optional paramater: round. Specify how many decimal places to round to, for example 0
{MEMBERRATING} - The member's rating. Optionally pass the paramaters round and formula... see here for details.
{MEMBERRATINGNUMBER} - The ranking ordered by member rating of this member.
{MEMBERLINKSVIEWED} - The number of articles viewed by the member, if tracking of article viewer names is turned on.
{MEMBERLASTVISITDATE} - The date/time the member last visited.
-- Optional parameter: date format, as with all date fields
{MEMBERFUNDSPROJECTION} - The date when the member's sponsorship funds can be expected to run out.
{MEMBERPOSITIVEPCT} - The percentage of trader ratings which have been positive.

Details of the member's usergroup can also be accessed through member variables:

{MEMBERGROUPID} - Id number of member's usergroup
{MEMBERGROUPTITLE} - The title of their usergroup as you've set it on your 'manage usergroups' page.
{MEMBERSECONDARYGROUPNAMES} - The titles of the user's secondary groups.
{MEMBERGROUPCANVOTE} - 1 if they can rate links, 0 if they can't.
{MEMBERGROUPISADMIN} - 1 if they're an admin, 0 if they aren't.

All other usergroup permissions can be accessed as well, just use {MEMBERGROUP + usergroup field + }.