Here's some artists I like, I tried to stay towards the lesser known
Bad Astronaut - alternative.
Belle and Sebastian - light indie rock
Bright Eyes - folky indie rock, especially check out the album I'm Wide Awake It's Morning
Cold War Kids - indie rock
Daniel Johnston - lo fi, folky, indie rock. You either love him or you hate him, but I think he's great.
The Darkness - rock. They sound like an 80s hair band a little bit, but i think they are actually from the 2000s
The Decemberists - indie rock
Elliott Smith - folky, sometimes acoustic, beautiful indie rock. If you want the simple acoustic stuff, check out the albums Roman Candle, Elliott Smith, and Either/Or. If you want the more complex stuff, check out the albums XO, Figure 8, and From a Basement on the Hill
Foxboro Hot Tubs - indie rock from the guys of Green Day, and it sounds nothing like them
Girl Talk - a mix artist, takes tons of different songs and mixes them together in a totally kick *** way
Gogol Bordello - they call themselves "gypsy punk" and are interesting and fun to listen to
Heatmiser - a grungy band from the 90s, though their best album is Mic City Sons, which is far less grungy than the others
Kathleen Balloon - she calls herself experimental pop I believe. Go to her website, myspace.com/kathleenballoon
Nick Drake - folk
The Pixies - Indie alternative
Polyphonic Spree - basically kind of a rock orchestra. They have 30 something members I think.
Reel Big Fish - Ska
Save Ferris - Ska
The Smiths - new wave alternative, also check out their singer Morrissey's solo stuff if you enjoy them
Sugarcult - pop punk
Tom Waits - Undescribable. Jazzy, bluesy, experimental...I'm not sure, but hes amazing
The Velvet Underground - folky, rockish, inspired Elliott Smith
Violent Femmes - alternative, they have super upbeat songs with sad lyrics most of the time. The songs are extremely catchy.