Latest Rockbox 3.14 on Sansa Clip Plus
Sansa Clip Plus is one of the most popular portable audio players. Although sound wise there are much better devices nowadays (and the clip is discontiued), the combination of price/small form factor and overall performance made it an absolute value for money. Rockbox is an alternative firmware that supports various media players. I will not go into details about it, but you should definately give it a try if your device is supported.