Octopart has a multi-vendoe shopping cart for your parts now, check it out -
While you’re searching for parts, add the ones you’d like to buy to your partlist. When you’re done, click the buy button to start choosing distributors you want to purchase the parts from. After you’ve made all your choices, you can checkout from each distributor from our checkout page. While we do not have direct online checkout available for all distributors, we will be adding more as quickly as possible. In the meantime, download a summary of the parts you are purchasing so you can place an order the old-fashioned way.
Cross-distributor shopping cart @ Octopart – [Link]