FL Studio is great for mixing, adding effects, the such. It's also good for creating your own songs.
We have a crack in the chit-chat section of the forum for the demo of the program that turns it into the full version. It also makes the following plugins usable without limitations-
-FL Studio downloader
-Edison Wave Editor
Anything not on this list won't work. o-o (But luckily, most of this is preinstalled with the demo)
Also, I'm not sure if the registry key will work once FL Studio 10 is out. (But it works for Ariella's 9.1, so as long as it's 9.something it will work.
What's great about FL Studio is that it's relatively easy to learn, and uses a very visual-based interface. You can add colors to tracks as another way of labeling them, and the mixer is rather easy to use- you can even use a limiter if the sound is making your eardrums explode.
Good effects to use are the Fruity Free Filter, set at 5074 (or something similar) frequency, high shelf (for males) or low shelf at 1027 (for females). This creates a human-like resonance sound in the vocal.
Also, Fruity Reverb doesn't hurt. Just don't over-abuse it. Doing so WILL ruin a song, and I only use it at it's default setting now. It adds a little bit a volume to the vocal track.
The Soundgoodizer is amazing for using VOCALOID and UTAU. In fact, set at setting "A" at the default amplification (which is shown by a ring of light around the plugin) is good enough for an off-vocal to have a bit more depth and a vocal track to have a LOT more.