List of Bitcoin forks or spinoffs
Forum user xorxor maintains a list:


http://bitcointalk.org/index.php?topic=134179.0



  A reason why the alternatives are better and/or worse?


The secret sauce for Bitcoin is how the proof of work approach allowed it to be a decentralized digital currency.  This approach allows "truth" to be determined by consensus of the network.  This also makes it vulnerable should the majority of the network not be honest. 

Keep that in mind first and foremost when considering any alternatives.