This とらいあんぐる☆Girl's Heart (Triangle☆Girl's Heart I think) by Shiki. I personally like this artist a lot. I wish I knew where to get a CD. That art for this video is also super cute.
This シンデレラ・ロマンス (Cinderella Romance) by Tatsh. Another great artist (who made Xepher in beatmania/DDR, yet another great song). The song samples Ode to Joy (Beethoven) for those who can't identify it (I know people who can't). Also has a very well done PV.
On a side note, I haven't played DDR in a while. I should.