Subscribed, thanks for making this
If you're feeling adventurous and want to try the actual Vocaloid software, here are some of the trials currently available (I'm sure there are more, especially from InternetCo*, but I need to look for them in they're weirdly formatted website).
*InternetCo is the company behind GUMI, for example.
(18/11/2015) Added trial for GUMI V4
(16/10/2015) Added trials for Hiyama Kiyoteru V4 and Kaai Yuki V4
(09/09/2015) Added trials for Hatsune Miku V3 English, Sachiko and V4Flower
VOCALOID2 Trials:
Hiyama Kiyoteru
Kaai Yuki
Nekomura Iroha
SF-A2 Miki
VOCALOID3 Trials:
Anon/Kanon (two Japanese female voices, scroll down until you see a small button with a lock sign on it. That means you need to login or register if you haven't already. You can then download the trial by clicking that button)
Aoki Lapis (same instructions as Anon/Kanon)
Chika (select "VOCALOID3 Chika" in the dropdown menu)
Galaco (includes two Japanese female voices variations. Same instructions as Anon/Kanon)
Gumi English
Hatsune Miku V3 English
kokone (select "VOCALOID3 kokone" in the dropdown menu)
Maika (Spanish voice + extra sounds like English "r")
Meiko Power
Merli (same instructions as Anon/Kanon)
Mew (same instructions as Anon/Kanon)
Tohoku Zunko
Tone Rion (same instructions as Anon/Kanon)
vFlower (same instructions as Anon/Kanon)
VY2V3 (male Japanese voice, same instructions as Anon/Kanon)
Yuzuki Yukari
ZOLA PROJECT (three Japanese male voices, same instructions as Anon/Kanon)
VOCALOID4 Trials:
Vocaloid 4 Editor 14 days trial (you need to be registered on the Net Vocaloid website)
Cyber Diva (English voice, you need to be registered on the Net Vocaloid website)
GUMI V4 (NOT the English voice. Each voicetype has two slightly different voices, useful for the Cross Synthesis function Vocaloid 4 offers)
Hiyama Kiyoteru Natural/Rock (male vocal. Natural has a softer tone with a falsetto high range, Rock is more solid and powerful)
Kaai Yuki Natural (young female child voice)
Megurine Luka V4X Hard
Nekomura Iroha V4 (Natural and Soft)
Sachiko (highly specialized Japanese Enka-style voice. Same instructions as Anon/Kanon)
SF-A2 Miki V4
V4Flower (same instructions as Anon/Kanon)
VY1V4 (has 4 Japanese female voices: Normal, Natural, Power, Soft. You need to be registered on the Net Vocaloid website)
Yuzuki Yukari V4 (Jun is basically her V3 voice, Onn is a softer, almost whispery voice and Lin is a more solid voice)
All the V2 and V3 demos include the actual editor you need to use them (V2 has the full editor, V3 has the Tiny version which has some limitations. In both cases the trials last 14 days).
Unfortunately there's no Tiny Editor for V4, but there's a 14 days trial available. Luka also comes with a .vst plugin called Piapro Studio which lets you use the voices as long as you have a program acting as a .vst host.