Most major music services provide the ability to discover music by listing related artists, albums and genres. The primary method used for this is text links which are clear, economical and efficient. Sometimes, photos are used in conjunction with the links to attract attention and provide an additional visual cue. However, this method, while effective most of the time, often obscures the relationships between the recommended items. Several services have cropped up over the years that go beyond the basic text style recommendations to provide immersive, visual environments to explore and discover music. Here is a collection:
TuneGlue
Last.fm and Amazon data power this mind-map style music visualization tool. You begin by typing in an artist name. You can click on the artist to reveal related artists and view album releases. Related artists float within the space and you can click on them to see their related artists, ad infinum. The interface is simple and clean but has some response issues. Another drawback is the fact you cant actually play music.
Dimvision MusicMap
This flash-based application uses a similar mind-map model but uses related albums instead of related artists. Each node is represented by circular album art, which makes the UI more informational and interesting than Tuneglue’s solid color nodes. You can select individual albums to get recommendations, album details, track listings, and purchase on Amazon. Major drawback: you can’t play music.
Gnoosic Music Map
Similar to TuneGlue, Music Map uses artist-based recommendations. After typing in an artist’s name you will see an expanding cloud of related artists. The closer two artists are, the greater the probability people will like both artists. When you click an artist on the map, the map reloads based on the new artist. The Ui is mainly text, load time is very slow, and there is no way to get more info or hear music.
Liveplasma
Liveplasma provides artist-based recommendations using a mind-map model. The closer a node is to your search term, the more related. The larger the node, the more popular. Colors are also used to show relations between artists. Liveplasma provides links to Amazon but no samples of music. If you register you can save your favorite artists and share your maps with friends. 
Musicmesh
Musicmesh uses audioscrobbler data to provide album-based recommendations. The nodes are represented by album art. For each album you can explore track-listings, play videos, read reviews, access Wikipedia info, and purchase on amazon. Play buttons next to track listings would make you think you can hear a sample instead of watch a video. Unfortunately, you cant control the size of the result set.
JSViz
Another album-based recommendation system using a mind-map style model. Nodes are represented by circular album art. Unfortunately, when selecting an album, the page reloads instead of expanding the node in place. You cant listen to songs and there is no additional information or links to purchase music.
Amaznode
This is a pretty cool tool for exploring Amazon’s product catalog. Just type in the name of an artist and select music from the menu. Amaznode will return a fairly large group of related albums. Each node is represented by album art. Rollover the art to see the name of the album and click it to get details, add to your cart or visit the related Amazon page.
Touchgraph
Another album-based visualization and tool for the Amazon catalog. Unlike many other examples in this space, touchgraph provides considerable control over the results both from a data and presentation perspective. The halo sizes represent the Amazon sales rank and similar items are grouped in colored clusters. You can also see nodes for genre and labels. Touchgraph provides detailed album information and provides a link to the related amazon page.
Music IP Playground
This flash-based site allows you to search for artists and see related albums by that artist. You can view and hear samples of individual tracks, get more information from other search engines, and purchase from Amazon. Unfortunately, the site does not show relationships with other artists or provide album recommendations from other artists.
MyStrands Playlist Mapping
MyStrands labs has created a tool that provides recommendations based on songs in a playlist. Once you select a playlist, MyStrands will generate a map. Orange dots represent items in your playlist while green ones represent recommendations. The closer the two given songs are, the better the recommendation quality they are for each other. The size of the node gives you an idea of how popular the song is (bigger nodes are more popular). Also, older recommended songs will become darker and darker (very old songs will be black). You can filter your recommendations by one or multiple genres. You can hear sample of songs but they unfortunately play in an eternal media player instead of inline.
MusicLens
Instead of using related artist/album information, MusicLens provides recommendations using a variety of audio characteristics such as tempo, gender, mood, etc. As you move the characteristic sliders up and down, MusicLens provides dynamic set of song results. You can restrict your search to specific keywords and genres, though the database doesn’t seem to be too large. You can play samples directly in the browser and purchase them from MusicLoad (Germany).
Burst Labs
A very slick flash-based application that allows you to visually discover music in the Burst catalog based on keywords, genres, moods and instruments. After clicking the discover tab, you are presented with a cloud of mood tags. Select a tag to dig deeper and refine your selection. You can rollover the floating nodes to hear the music directly in the browser or link to details. From the detail page you can download digital versions of the songs (login required) and link to similar songs. Unfortunately, the search result page shows composer names instead of artist names, which makes browsing by artist a little difficult.
Playola
Playola is a music similarity browsing tool. You can find new music by moving around in a music “space” and listening to songs (or short clips) that are nearby in the space. Recommendations are given based on various audio characteristics. As you listen, you can give feedback on whether or not you agree with the similarity matching. Playola allows you to tweak various audio “dimensions” to change the resulting set of matches. You can listen to samples and even hear a sample playlist containing all artists in the results.
Kartoo
Kartoo is a visual search engine that works very well with music. When you enter a term, Kartoo analyses the request, questions the most relevant engines, selects the best sites, and places them on a map. You can infer the relevance of the results by their position on the map. When you rollover the result icons, you get a preview of the site in the upper left pane of the window.
Other Projects Worth Checking Out:
Search inside The Music
Radio Protector
MusicMiner