Ill try to suggest to appeal to a large base of interests and genres. I wont mention the obvious - everyone already knows who Daft Punk and Pink Floyd are.
Girl Talk - entry level mash-ups.
http://www.youtube.com/watch?v=LEE00OqOjgI&feature=relatedPomplamoose - good indie pop, the lead singer has a unique voice, Youtube videos they make show how they record it all from an apartment studio.
http://www.youtube.com/watch?v=7jM2YwhaNCc&feature=SeriesPlayList&p=DE53A978215C0424Ratatat - Elctronica/some hip-hop elements - give the album
Classics a listen to
http://www.youtube.com/watch?v=64liF2VuLxIHallucinogen - Insanely well made techno/trance music. surprisingly inspired by drugs.
http://www.youtube.com/watch?v=8bXh3KkOzxcHird - Great lounge/Jazz and Trip-Hop music,
Moving On is the only album released so far, but this man is a genius.
http://www.youtube.com/watch?v=tX-4gbQ8fQMBlack Eyed Snakes - jazz/blues rock - just released there first self-titles album - think soundtrack from Black Snake Moan
http://www.youtube.com/watch?v=mrCE-QFrxmgThe Avalanches - great mash-up/electronic group from Australia,
Since I Left You the one and only album is great even if you dont like mash-ups - Frontier Psychiatrist being one of the better known songs.
http://www.youtube.com/watch?v=U8BWBn26bX0fun. - Some indie pop, good listen even if your not into that kind of music. The debut album, Aim and Ignite is great, hope they get signed to a major label.
http://www.youtube.com/watch?v=SIL8ejMden4Werewolf Congress - more entry level mash-ups, uses MC chris well with other music.
http://www.youtube.com/watch?v=UwwDmZd1_0AFour Tet - Solo project from one of the guys from Fringe - good mix of post-rock, prog-rock, and electronica.
http://www.youtube.com/watch?v=M2dPYRhSb4cPendulum - great techno and dance music - Hold your Color is a grand album.
http://www.youtube.com/watch?v=ZCKpzP5SGYw&feature=relatedThe Flaming Lips - Great Progressive-rock - very upbeat -
Yoshimi battles the pink robots and
Embryonic are a definite must-listen.
http://www.youtube.com/watch?v=2F8EAv8jSWEThe Next Door Neighbors - Great folk music made by two girls from Oregon. Lyrics arnt bad either.
http://www.youtube.com/watch?v=wHgCKjN5ZfwClare & The Reasons - more indie pop music. The Movie is a good album.
http://www.youtube.com/watch?v=ptgSD2ilzEoEdit: finished youtube links