Dave-
I listened to "Monster Machine". My first suggestion would be to try encoding your mp3s at atleast 128kbps, there's a lot of washy sounding cymbals and other mp3 artifacts that detract from the quality quite a bit.
I don't really care for the guitar tone, it sounds too much like it was recorded through a j-station or something similar. It also seems to get lost in the mix in a few spots, and its hard to make out what the guitar is doing. You might try turning it up a little, or EQ it differently or something. I do like the non-distorted guitar part though.
Good job on the vocals and backing vocals, i'm diggin those.
Nice job, thanks for sharing!
travis