With the taking off of Podcasting, it was just a matter of time before the mix tape found an online home. The Wooster Collective is one such repository, featuring the Vitamin_F Series curated by Vinnie Ray. The latest mix is compiled by Maya Huyak and is 74 minutes (35 mb) of quality "eclectica".
My personal favorites are the starters by X-Ray Specs and Julie Ruin (of Le Tigre) and the 1-2-3 punch of Mellow Candle, Nanette Natal, and Olivia Tremor Control. And if you've never heard the Langley Schools Music Project, now's your chance.