Also, funny, was just posting about this yesterday! The 30-day pre-sale for batch#2 of the Siacoin ASIC just went live today:
https://obelisk.tech/
If you're thinking about hopping in, I'd advise waiting until the last day of the pre-sale, as the profitability of these units will be directly tied to how many are sold in this second batch.
At the current Sia price, assuming only one unit sells you'd be making $128/day (when they ship these in August), paying for itself in a matter of ~2 weeks. If 5,000 units sell then you're down to $50/day, making it more like a month before you're in the profit. If 10,000 units sell, you're down to $30/day AND you're not likely to hit profits before they ship the 3rd batch, which could stretch the amount of time before you hit a profit by months. If it's 15,000 or more, you likely won't ever hit profits at the current price.
3,516 units sold in the first batch, for reference.