Question: I'm 20, about to graduate college, and have accepted a promotion at my current job that after taxes will leave me with about $25,000 not allocated to anything.

* I am already putting aside 15% of my income towards retirement.
* I have no consumer debt, as I use my credit card as a debit card with money set aside for the float.
* I have no student loans, as I have paid out of pocket for everything (and have been reimbursed tuition this year because I ended up with more scholarship money than I needed).
* I have been building up an emergency fund, and am currently at ~30% of my goal.
* I'm living with a roommate in a fairly low CoL area.

What is the best thing to put this money towards? I've considered saving up for a down payment on a house, as well as putting aside money to eventually replace my car from 2008, but I'm not sure if there are better options at this stage.

Answer: 
Both of those options are great. Houses are a great wealth-builder, and replacing a car with cash instead of a car loan is a great option as well.

My first thought would be to complete your emergency fund.

After that, it depends on how long you think your car can last, and how long before you plan to buy a house. It generally isn't recommended to "invest" money if you need it in a year or two unless you're willing to risk 10-20% downside in that period for the chance of 30-40% upside. If you plan to spend it in a year or two, then a high-yield savings account or money-market fund would be a reasonable choice. Past that, look at tax-advantaged accounts like IRAs, or even HSAs if your company offers it. HSAs are tax-free, and they can be used before you retire on qualified expenses. It requires a high-deductible insurance plan, but the lower premium of these usually more than makes up for the difference in deductible. Plus if you have an HSA and a good emergency fund, paying that deductible (if you even need to) should not be a catastrophic event.
You don't need to put it *towards* anything in particular. There's no requirement that a pot of money has to have a label on it saying what you're going to use it for.

If you invest it in a diversified investment fund, it can sit there until you decide what you need it for. That could be a car, a deposit on a house, or it could stay there until you retire.