I came across
THIS blog and have had a chance to check out many of the sites. For free and legal tracks, I haven't found a better resource. Not many artists that are signed release free and legal album downloads, but many discussed on these boards do offer up a free track or two. If you don't mind listening to music not in the context of a complete album, these are the sites listed in the blog that I feel are worth the time (NOTE: I'm really only looking at the Compiled Lists/Blogs part of the linked article):
1. Download.com Music - I'm not sure why the author buried this one on his list, as it is my number one daily stop. Well organized with tons of choices across a wide variety of genres, no other site listed churns out as many tracks daily. Almost all tracks are at a respectable 192 kbps as well.
2. insound - Great back catalog and they offer up many free tracks that I don't see anywhere else. They like to add tracks on new music Tuesdays. Watch the MP3's though. I've seen everything from 320 kbps to 32 kbps.
3. SXSW - Talk about a lot of stuff! I only downloaded the individual tracks that I wanted, as I am in the process of reorganizing everything I have and didn't feel I had the time to sort through everything if I downloaded the whole lot in a torrent. Some good tracks for all years by some artists that I haven't seen offer free tracks elsewhere (Genghis Tron and Circle Takes the Square are the first to come to mind). Tracks for 2005 and 2006 all seem to be at 128 kbps, but 2007 tracks vary a bit.
3. betterPropaganda - Many of the free tracks here are available at the first two sites listed (I think this site actually links to the MP3's on insound). There are some tracks here that are exclusive though, like The Magnetic Field's California Girls and the Neon Neon track. Worth checking out.
4. 3hive - Great back catalog and probably the best search system of any of the sites listed, but activity seems to have slowed on this site and many of the free track links are dead. After I got what I wanted from the back catalog, I don't go to this site very often.
5. Fingertips - Nice blog where the author picks 3 of his/her favorite free downloads for the week. Really digs for these as well - in the last month or so, I haven't seen anyone else with the Fleet Foxes track.
6. Epitonic.com and Salon.com - Neither are adding new tracks, but they have their back catalogs still available. Both are well worth that one time visit to grab what you want. Salon.com has some dead links, but most everything on Epitonic was still active.
Other quick notes, Free Albums Galore looks promising but I haven't had the time to fully explore it. Largehearted Boy has a lot of free live track links. CMJ has some decent stuff, but not very much apart from the Kevin Drew track that I haven't seen elsewhere. I grabbed some free Mastodon tracks from stereokiller, but I know almost nothing about most of the bands listed so can't comment much on this site besides it seems to focus on metal, emo, and hardcore punk. MTV.com has some New Pornos, a Vampire Weekend, and an Aesop Rock track; and Amazon's selection is pretty pathetic compared to what they used to offer.
Here are some sites not listed that I find worthwhile:
Stereogum - Usually my second daily stop. They have some fantastic free downloads. They seem to get the newer stuff first and have a lot of exclusives that I haven't found elsewhere. Even the articles are worth a read if you have the time.
RCRD LBL - Well organized with some exclusive tracks by Born Ruffians and Quinn Walker, among others. Not worth a daily visit, but definitely worth checking out every now and then.
Spinner, Filter, Popmatters, Pitchfork all have media links where you can download free MP3's, and all of the sites make it a pain in the ass to find something in the archives. I didn't bother going back too far, but just started checking these sites a couple of times per week and downloading anything that looks interesting. Many of the links at Popmatters and Pitchfork go dead relatively quickly.