My current rental properties were both financed with hard money, before paying them off low enough to get a HELOC and simply put the balance on there.I'm now interested in purchasing an additional rental property (4-plex) through a traditional lender, as the 10% interest rate is crushing. 

Since you own your own home a HELOC to pay the down payment might be the easiest option.

I thought about using a HELOC to be able to put 10% down on a duplex because in the areas where I would want to live most duplexes require a Jumbo loan (425K+)I would love to hear your thoughts and what you would do in my situation, from the creative to the boring. 

they also do helocs for rentals (up to 4 rentals) as well. 3% 1st 6 months % 4% thereafter; $50 annual fee. 75% LTV.

It is very personal and has nothing to do with how others prefer to view themselves and approach their investingI started my investing with a HELOC, but only after paying off my personal residence.Purchased Rental #1 all cash.

The home was appraised for the lender using comps when I got a HELOC last fall around $50,000.

@Margie Pierce  We had a HELOC with a bank that failed. 

HELOC, personal line of credit, credit cards etc.

Continue enjoying nice returns, principal accumulation, debt reduction and accept that I'min a great market that's not likely to go drastically South anytime soon.Sell and Reinvest:  Realize quadrupling your initial equity investment is damn good, take advantage of this market and invest in a bigger property, ideally through a 1031 (note: I don't have anything lined up yet so pulling off a 1031, especially in my current market of Seattle, might be tough).Hold, Cash-Out Refi: Refi the property at a lower rate and take out some cash to us for future real estate investments that my wife and I plan to make in the next 3-6 months.Hold, obtain a HELOC: See if I can get a HELOC lined up so that we can access funds when needed...although I have no idea how interest rates here would compare to the cash-our RefiI know that I'm hitting on some general, differing philosophies of RE investing, but curious to know if folks out there have some opinions?

Finally, you could also use a HELOC to do a flip or another project.