With external SSDs, the main advantage over hard drives (HDDs) is clearly the speed. In addition, SSDs are also usually available in smaller form factors, which is more convenient for transport. An SSD (Solid-State-Drive) also has no moving parts and is therefore more shock-resistant. The only downer is the price. However, as this has been declining steadily over the years, SSDs could soon displace the hard drive from your throne.
We have external SSDs from Samsung, Sandisk, WD, Angelbird, G-Technology, Freecom, Kingston, LaCie, Seagate, Toshiba, Transcend and Verbatim.