Google Sites is a free and easy way to create sites. Get a Free Google Sites Shopping Cart Here
If you want to host your store for free with them, perform the following steps:
1. Define your Store ID using this instruction: How to get your Store ID
Your store's google gadget URL is https://app.ecwid.com/jsp/STORE-ID/gadget-v2 , where STORE_ID is ID of your store. For example: https://app.ecwid.com/jsp/1003/gadget-v2
2. Go to http://sites.google.com/ and log in with your Google account.
3. Press the Create new site button.
4. Setup your site's template, name and theme. Press the Create site button.
5. New site will appear.
Create a new page using "+Create page" button if you want to have a separate page for your Ecwid store. Then press "Edit page".
6. Go to Insert → More Gadgets menu. The popup will appear.
7. Press the Add gadget by URL link.
8. Insert your gadget URL (you've defined it at step #1) and press Add.
9. Enable "Include a scrollbar on gadget when necessary". Disable "Include a border around gadget" and "Display title on gadget". Increase the value of the "Height" option.
10. Press OK to add a gadget, then press Save to save the page changes.
That's all! Your Ecwid store is installed on Google Sites.