I love HeroClix.  I blogged about my team a bit back.  How about a feature about HeroClix in general?  (all of these pictures come from WizKids, the maker of HeroClix.) http://www.WizKidsGames.com

To me, one of the awesome things about this game is the variety of characters.

HeroClix is, on the simplest level, like chess with superheroes, except that if you want to play with 4 bishops and no knights, that’s not only OK, it is encoraged.

To play, you need pieces, a map, dice, and something to mark your pieces with.  For a complete setup, you could start with the new Legion of SuperHeroes starter set.  It includes everything you need and a complete up to date rules book.
http://www.wizkidsgames.com/heroclix/dc/gameresources.asp?cid=41258

Let’s take a look at the centerpiece of Heroclix, the dial.  You will notice it has an L shaped slot.  There are 4 numbers in it, and one more printed on the dial right above the L.  Lets start at the top of the L, move down and then right. 
1. Movement = how many squares you can move.
2. Attack = how likely you are to hit
3. Defense = how likely the opponent is to miss
4. Damage = how much damage you do on a successful attack.
(and the number printed on the dial)
5. Range =  how far away you can attack.

To make an attack, declare your target.  Then roll 2 six sided dice.  Add the total on the dice to your attack value.  If this number is equal to or higher than the defense value of your target, you have successfully hit.  Damage is now dealt.  The owner of the target piece turns its dial the number of clicks of damage you have done.  As pieces take damage, the values colors change.

How do you decide which pieces to use?  This is called building your force.  There are two other numbers, near the edge of the ring.  the larger number is the "point cost".  the smaller one is the number of the piece in the set.  Usually a force is built to a certain point level, in increments of 100.  A typical game might ask for a force of 300 points.

What about those colors you ask?  The colors represent superpowers characters might have.  There are a whole range of these, from phasing to superstrength to invulnerability to outwit.  That is what makes the game work for characters as diverse as Superman and the Joker.

Follow this link to a complete list of powers.
http://www.wizkidsgames.com/heroclix/documents/DC_LOSH_PAC.pdf