equipment recommendation - Can you recommend a macro lens for a micro 4/3 camera?

I've recently purchased a micro 4/3 camera (Panasonic GF1), and I'm aware that with an appropriate adapter, I can use a large variety of third-party lenses.

I'm interested in experimenting with macro photography, and I'd like to purchase a reasonably inexpensive macro lens (2nd hand is fine) from ebay to allow me to get my feet wet.

1. 
   
   

   Are there any particular brands or models that would be worth looking out for?

   
   


2. 
   

   Are there are any limitations with the micro 4/3s format, that I should be aware of when purchasing a third party lens?