As terrific as Ubercart is for turning your Drupal site into an ecommerce powerhouse, there's a lot of additional modules that can extend its functionality. Here's a quick look at just a few of them:

Donations - want to accept donations from you site? Among other functionality, this module allows you to create a "product" where your donors to specify the amount they'd like to contribute.

Multicurrency - while Ubercart doesn't have the strongest set of international features (yet), this module can help get you going in the right direction by displaying prices in your customer's local currency.

Recurring Payments - want to set up a subscription service where you can charge your customers a fixed price each month? This module, when combined with a compatible payment processor will do the trick.

Keep in mind that modules are all in various stages of development (and stability). Your mileage may vary.