I'm currently looking to upgrade my SD Card to a larger size, whats the current size limit? and when can i expect releases of larger capacity cards to come out?

Current largest sizes are 4 and 8gb units

But check with whatever product you are using it with as sometimes older products will not be able to see the whole 4 or 8gb  

hope that helps

jamesh is right 4 and 8gb are the largest. I also depends on a card format