There have been a number of threads recently requesting ANet to add various forms of new storage. It's very unclear if that's likely to happen, never mind when. So here's a list of eight different options for increasing storage right now, comparing the cost per slot.
Second best depends on what works for you:
Other alternatives are less convenient or outrageously priced
And of course the best option is always: change your inventory management habits: storing less means more time for you to play the game.
I'll go into gory detail about these options in the first follow-up post.
Hype is the path to the dark side. Hype leads to unfulfilled expectations. Disappointment leads to anger. Anger leads to disgust. Disgust leads to "oh, new shinies! I'm back!"