Portable speakers are a dime a dozen these days, running the full gamut of prices from $30 to $300 (and likely beyond). They come in all shapes and sizes, too - from the small Satechi Swift to the almost-a-boombox Jambox Big. Short story long, there are many to choose from, no matter your requirements.
The most well-known is the Jawbone Jambox. It puts out solid sound, comes in a portable and attractive package, and has good name recognition.