For our first product, we used eBay, starting an auction at $0.01/free shipping and letting it go for a week to see where it ended up. We got lots of bidders and a better price than we expected, and most importantly lots of interest.

After that, we did several more eBay runs to test different copy / pricing, and then with that information, launched our own web store (normal fixed-price checkout, non-eBay) about 8 weeks after that first auction.

Now with 2nd product, we've already got an established reputation and traffic in our niche, and developed the 2nd product specifically around the feedback we were getting from customers.

This is for a consumer product, hybrid of physical parts + content. Not sure that you can apply the eBay concept to a SaaS, but depending on what you're doing, it may actually be possible (i.e. if people would be naturally searching on eBay for software to fill that need, then put up a 12-month subscription as an auction!).