There are three bands with the name Riverside:

1. A progressive rock band from Warsaw, Poland. It was founded in 2001 by Mariusz Duda, Piotr Grudziński and Piotr Kozieradzki, who shared a love for progressive rock and heavy metal. Following their 2003 debut Out of Myself, the band were signed by major prog label InsideOut, releasing 'Second Life Syndrome' in 2005. Riverside's music has been described as a mix between Opeth, Pink Floyd, Anathema and Dream Theater, containing long, ethereal keyboard-laden passages and heavy, crunchy metal riffs. 'Rapid Eye Movement', the latest Riverside album, was leaked on the internet in August 2007, and has a release date in the end of September in Europe, October 09 in the US. In the summer of 2007 Riverside supported Dream Theater in the European leg of their tour.
Official site

2. A 90s alternative rock band from Pennsylvania that played jangly music along the lines of the Railway Children and the Ocean Blue, yet incorporated a dream pop sound similar to For Against. Their first album, One, was released on Sire Records in 1992, and their second album, Taste, was self-released around 1994. The Official Site of this band is http://www.riversidetaste.com.

3. A country rock band formerly known as Riverside Avenue from Missouri, USA. They were active between 1980 and 1990. They re-formed in 2001 and released the album Simple Life. Part of the proceeds from this release are being donated to the Relay for Life and MS Foundation.