My favorite method is one that Jonathan C touched on briefly -- find agents who work with investors. This is far and away the best method for me and especially for new investors.
You become the person who is essentially creating pocket listings for the agent's clients. This makes you increasingly valuable to them and they'll be happy to pull endless comps for you, knowing that you won't be using them to purchase properties. So be honest and they'll understand that it's worth helping you. And how do they make money? They bring your deals to their investors. When those investors finish rehabbing, they list with that realtor who brought them the deal!
I have a great realtor who drives to the properties with me and lays out the numbers for where I need to be to purchase the property and make my fee. The entire process of wholesaling to an investor is done for me. I take calls from my marketing and pass it along to him. He does just about everything else.
Like most new wholesalers, I put rehabs on my first property at only $5k. I now have a better idea of what it'll run for, having walked through several properties with my agent.
I would recommend NOT creating surveys for investors to fill out. What I've found is that they basically want a deal that is either:
a) 70% - rehab
b) All rehab and costs included and minimum $20k or $30k profit (better for a $150k property, not a $400k property)
c) Minimum 12% cash on cash (best when showing cash vs hard money and both being above 12%)
I don't like asking them questions anymore without a deal. I present a deal and they tell me why they like it or they don't. Essentially, if they buy it, they like it. If they don't buy it (and it's a legit deal) then I ask why and they tell me.
And you'll find more flippers in some areas, more cash flow investors in others. In Seattle, cash flow investing isn't so great but flipping is awesome. I like cash flow buyers because they have fewer fees so it's easier to find a deal if it's tight.
By the way, DO NOT bring MLS deals unless they're MUCH cheaper than listed. Your reputation matters a lot! Your value proposition as a wholesaler is bringing them off-market deals they can't find anywhere else.