From the wording of your question I'll assume that you mean only USB 2.0 devices. The search phrase you are looking for is "USB powered", here is one for example: http://www.newegg.com/Product/Product.a ... 6827106389
Unfortunately that search will find those having both one or two cables, you have to look at the unit itself to see that it has only a single USB connection and no separate power connector. Note that true USB powered (single cable) drives would include only readers, as drives with burning capability would use more than the 2.5W power that USB 2.0 can deliver. In otherwords, if you limit your search to DVD-ROM drives only you should be able to find those that are truly "USB powered".
USB 3.0 can deliver 4.5W so USB 3.0 external "USB powered" drives are available in writer (burner) versions: http://www.newegg.com/Product/Product.a ... 14J0PB0834
Unfortunately even most slim-line writeable drives draw more than 10W so many if not most USB 3.0 burner models will still require dual connections (or Y-cables) in order to supply the necessary power. Scott.