If you haven't been picking these up as they're announced, Amazon decided to finally give you a way to get all 25 with one click over at their 25 Days of Free page (amazon.com) - scroll down past the days to find the checkable list and "Buy selected song" button.
Oh, one more thing - if you're GIFTING MP3s, Amazon says that you can get $2 off with the code GIVEMP3S. Details about THAT over here.
What we have here is a Grooveshark playlist of 20 songs which it looks like I played a whole bunch this year. iTunes says they're all from 2010, which means I hope I/whoever entered the correct year at the time I picked up these songs.