1) Invest into CPU/GPU/FPGA mining is not an option anymore, you will not earn you invested money back.
2) Only option left is to buy ASIC. There are few companies that produce them, but:
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Avalon. There are rumors that batch 4 of their devices is coming for sell. This might be profitable, it depends on price they will ask for ASICs). But, they fail to ship ordered batch 2 and 3 devices for few months now. I would invest in batch #4 only after confirmations here on forum that batch #2 and #3 devices are delivered.
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Butterfly Labs. Only few people recently have received orders from last year. And it is unknown when everybody else will receive them. Anyway, it will take months for BFL to ship current orders after they will start, and few more months to process new orders. If you will order ASICs from them now - you can expect to wait at least 4 months before delivery. Good news is that even in this case you should get some profit, but expect at least another 4 months for roi.
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KNCminer. They seems to be legit, but no working device prototype is shown yet. Good news is that they promise to start delivering products in autumn, with instant delivery of new orders.
- ASICminer. They sell ASICs with instant delivery, but roi for them is smth like a year in a best case, do not mess with this.
- Custom created mining devices from chips (Avalon and BFL produce and sell chips with btc calculation logic, but electronic boards are not sold for them). It's kinda tricky. Companies with certified engineers spend months trying to create working boards that will work with these chips. And some people promise to do the same in their garage. I can't believe they can do this so easily. Anyway, you can search this forum for topics where people sell complete clones of Avalon devices and order, I think these devices will be worth it.
- everything else is a scam, if will not be proven else.
So, I would do smth like this:
1) Buy all custom created Avalon copies from this forum
2) Invest half of money left into Butterfly Labs (50%)
3) Wait for Avalon actions. If Avalon will ship devices from batches #2 and #3, and will start to sell batch #4 - I would invest half of money left (25%)
4) Wait for KNCminer actions. If they will start to ship existing orders, with minimal delay before shipping new orders - I would invest all money thet left (25%)