"Ai Dee", a catchy song with great vocalization by Miku. A major selling point of this song is Luka's amazing rap, in English too.
"Ai Kotoba /Love Words II", an upgrade of sorts to the original version; both songs tell the story of a girl who gives her thanks to the ones that have loved her all this time. As usual in some of DECO*27's songs, puns are hidden in the Kanji; most notably, Ai Kotoba (愛言葉) is a play for the kanji of "Password" or "Aikoboba" (合言葉).
"Ako'y Nasaktan" ("I'm Hurt"), an original Tagalog melancholy song about the pain of a broken heart, by the same composer of "Let's Party Tonight" and "Sa Piling Mo".
"ALICE iN BLACK MARKET", which uses Miku's Solid and Power Append banks to create a heavy yet catchy song. There's no consensus what it's about, but it seems to be about her mentally dominating a guy for sex.
Special mention goes to the development. The creation behind it was originally just going to be a mash-up of "Love is War" and The Miz's "I Came To Play", but ended up including a little bit of everything; CM Punk's "This Fire Burns" while he was in the Straight Edge Society, the opening guitar of Batista's "I Walk Alone", with bits and pieces of Randy Orton's "Voices", and more. However, the "I Came To Play" bit at the end is probably the most AWWWWWWWWESOOOOOOOOOOME moment of the song.
Her cover of Kyary Paymu Paymu's "Candy Candy". Amazing tuning of her Append Solid bank to make her sound quite different and quite human. Here's another version by the maker of "Let's Party Tonight". And now here's an English version by her English voicebank, which is just as cute.
"Drain", a song by ELECTROCUTICA that has a clean and professional edge to it, but blends that clinical precision perfectly with soothing rhythms and mind-melting beats along with catchy little piano tunes and very clear, sharp vocals. Those with weak hearts, you have been warned.
Cover of "The Dragonborn Comes" from The Elder Scrolls V: Skyrim by her English voicebank. Not only does she sing beautifully, she then sings part of the game's main theme that's the Dragon Language. And there's also the awesome PV featuring Miku herself singing next to the piano player.
"Earth Song", a beautiful blending of all her append voicebanks.
"Eazy Dance" (misspelling is intentional) is made by the same producer as "Freely Tomorrow", Mitchie M, and is a just as awesome dance tune. There are two moreversions with awesome MMD P Vs by Raiku-P.
"E-iRO" Amazingly, this song is calm, somewhat sad, and a bit upbeat all at once. It's hard to explain.
"The Forgotten Song" by whoo is absolutely beautiful. Miku's voice sounds great in it, and the indie-esque feel is something you don't find often with Vocaloid. For more eargasms, listen to this remix.
"Goddess of Spring". A very beautiful and haunting song featuring a wonderful animation of Miku playing the harp on a small island in the middle of a lake in a forest under the moonlight. And especially haunting is the ending where the camera views Miku's reflection in the water, but as it pans up, she and the harp are gone, leaving an empty seat. A somewhat low resolution CG version with English subtitles, but where Miku can be seen to be noticably breathing, can be viewed here.
"I=Fantasy". It was only a matter of time before Miku covered SeeU's demo songs, and in Korean too.
And, of course, the famous leek spin video featuring the song "Ievan Polkka". Strangely addictive, you could watch Miku spin a leek for hours to this song. Even better, here's Miku singing the '"entire Ievan Polkka in Finnish"' (not just the "leekspin" portion)!
"Lynne" is brilliant as well. Make sure to check out the unofficial PV as well.
"Marionette Syndrome" and "Marionette" both have completely different messages, but are good. Be sure to check out the Nico Nico Chorus version of "Marionette" as well.
"Melody.exe", an old classic, but still very good.
"Melody Line", with another good MMD video by Wakamura.
"Melt" is very cute, upbeat, and romantic song of how she sings of her crush and her inability to tell him how she feels. There's also a boy's lyrics version, making duets possible. Another PV adds an extra layer of awesome (skip ahead to 3:30).
"PlusMinus". Really, no written description does the song justice. No, wait, NOW no written description does the song justice. Haruami is also an amazing song in this remix. Leave it to Yuyoyuppe to make everything better.
This cover of Lady Gaga's "Poker Face" is probably one of (if not) the best efforts by anyone to make Hatsune Miku sing (and RAP!) in clear and understandable English. Here's the same song but with more suitable video footage.
"RuRaRa", a catchy tune, also featuring an MMD video of instrument playing Vocaloids (including Kaito, Haku, and others on those instruments).
"Sa Piling Mo", a very catchy original Tagalog composition (from the same composer of "Let's Party Tonight"), which in fact also serves as the OP for the creator's other main project, "I Love Him", a fanmade TV sitcom style series featuring the Vocaloids themselves as cast members. A preview of the show can be viewed here, and OP version of the song complete with video can be viewed here. The entire OP video done in MMD is a great effort in its own right.
"Sadistic Music Factory" is another great piece by cosMo, it's both creepy and catchy. Miku can be scary when she wants to be.
"Sakura Uta So", an immensely beautiful song with amazing and almost realistic vocalization, even from Miku's original V2 voicebank.
"Shoddy Utopia Policy" by Suzumu, tuned by CircusP. What is amazing about this song is how all Miku's appends are used, and how the back-up Vocaloids are integrated into the song, it's a prime example of "teamwork" for Vocaloid songs, even with Miku as the main singer.
Here she sings a roughly translated Japanese version of "Still Alive" from the game Portal. And here's her cover of "Want You Gone" (also from Portal). Her use of the Soft append makes it actually suitable.
"Streaming Heart" by Deco*27. A catchy song apparently about a guy whose relationship with his girlfriend went south because of his addiction to Miku. And how he got gloriously rejected by said girlfriend in the end.
"Sweet Devil", one of Hachioji-P's most notable works, telling the story of a girl who plays with men's hearts. Ignoring what the song really is about, this is still one of those earworms you'll get addicted to once you hear it.
"Sweet So Sweet" is thick, heavy but also abrasive and simultaneously engrossing. The sharpness of Miku's voice complements the guitarwork in a really cool way.
"Tell Your World defines what the Vocaloid fanbase intends to do by releasing their works across the world.
"Time Machine" by a team comprising of 40mP, 164, and daishi. A moderately paced melancholy song about the pain of separation. The impact of its Tear Jerker-ness can really be felt in the PV featured in the game Project Diva F.
"Tokyo Endroll" is one of the most underrated Hatsune Miku songs and probably the best Vocarock song as well. A theatrical synth string section with a steady, 50s American rock-esque rhythm? Yes, please! They do so much to make the song sound as absorbing as it is. And the chorus...!
"Tokyo Rock City" has been given many covers notably Valshe, and it is worth a listen.
Cover of Carpenters' "Top of the World" by her English voicebank. With an adjusted key to suit her voice better. The result is well made.
"Top Secret" by SCOP is a wonderful, wonderful song.
"Torinoko City", also known as "Left Behind City" has a catchy rhythm, really good use of Miku, and deeply meaningful lyrics. Certainly one of the best Miku songs out there.