As a non-homeowner who may want to own a home someday, this topic is sufficiently near to my heart that I went ahead and incorporated it into my IPS. For me, that helps me not think about it and actually live my life.
My perspective, as someone who isn't a professional investor and doesn't want to be one, is that the only instruments that aren't correlated with the stock market that are worth considering are savings accounts, CDs, and bond funds (and even that last one is dicey). Screwing around with options and preferred stock funds wouldn't be worth it to me at all.
If one accepts that premise, the question would then comes down to whether you “need” the money in three years or could stomach some fraction of it evaporating in market shenanigans. If the former, CDs are really the only way to go.
If you are comfortable with the risk, I agree with L.A.S.: If Vanguard (or whomever) has a muni fund in your state, it seems like a great option. But last I checked (it's been a while), muni funds didn't yield enough to be worth it for me and my tax situation — CDs came out ahead after-tax.
An even simpler option: if your annual compensation is $250K and you're on this forum, it seems like it shouldn't be that hard for you to come up with $180K when you need it? So you could just mix it with the rest of your post-tax funds wherever they normally live, and assume the money will be there when the time comes. Sure there may be a couple of down years, but none of us know which years those will be and if you're still getting paid during that time (a big "if" for me, maybe not for you!) then you could always just stop funding your post-tax accounts until you've saved up the capital?
But I do get the appeal of having cash to buy a beach house during a recession — unfortunately, market timing is just a fact of life when dealing with real estate.