One is in use by GMC (General Mining Corp) and GRF (General Retirement Funds). As their value and/or price is not specifically tied to or pegged to BTC, they exerience potentially greater flexibility in this kind of application. (If their investments/loans fail, their value in terms of other currencies (such as, for example, BTC) might well fall.) Both GMC and GRF provide secured loans featuring associated repossession agencies.
Another is mortgaging your BTC. That is, put BTC up as collateral for loans denominated in things other than BTC itself. This approach can be used for such things as borrowing fiat to buy BTC which in turn can become more collateral to borrow yet more fiat to buy yet more BTC and so on. (Careful of margin calls in doing that, of course.
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-MarkM-