OK my post about Google Base was only three days before they officially launched so here's a prediction that's a little farther out...
Google Wallet or perhaps Google Money. Lookout paypal because I believe that Google may be looking at changing not only how we find things on the web but how we pay for them as well. Google Base or "First Base" as it's being called allows people to post arbitrary data on the Google base website. This can be collections, photos, text, descriptions, products, etc.
Second base is likely the ability to pay for these things and advertise for them. Remember that even though Google is a search engine it's business is driven through ads. What's the best way to increase those sales? Flip the ebay/paypal/amazon model around. Allow individuals to post and sell items at little cost then charge a small fee to advertise the item.
I expect something similar to paypal but far more open in it's design. I'm guessing something in 6-8 months. We'll see how this prediction holds up.