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Both the heavy bone and glob of ectoplasm are going to skyrocket in price after the crafting 500 patch. So get on those now, but avoid the glob of ectoplasm unless you're already rich. They are quite pricey! That's why I'm recommending the heavy bone in the same sentence, because it provides a much cheaper alternative.
I purchased 50 gold in Glob of Ectoplasm today and 25 in heavy bone. Here's hoping these among the many other speculative items explode after the crafting 500 patch.
For a list of items I've recommended thus far, try these:
Also check out the private forums under Speculation for even more items to invest in. The one item is literally something everyone needs but I've yet to see ANY website mention it as something worth stockpiling for the next patch.