In Washington state, it's officially 24 ounces and 15 plants. That's a lot of marijuana.
In Holland, by the way, you're only allowed to have 6 plants. And a "coffee shop," the place that legally sells marijuana, is only supposed to hold 16 ounces at any given times (but for practical reasons, that limit is often ignored).
Here's the article in the Seattle Times about what is now the legal limits for a "60-day supply of medical marijuana."