Enable the "Special Offers" block at admin/store/settings/catalog/edit, then make the product(s) you want to feature "sticky" by selecting the "Sticky at top of lists" checkbox under node/#/edit where node/# is the product page for your product. There are some more settings for this block at admin/store/settings/catalog/edit/blocks

The "Special Offers" block can be renamed or repositioned at admin/build/block (Actually, right now it can't, because there's a bug in uc_catalog which I found while testing my response to your question!. I've just reported it at http://www.ubercart.org/issue/2902/uc_catalog_error_special_offers_block and I'm sure it will be fixed promptly.)