Tips for Recording

Options for recording and uploading
Vocaroo.com is alright but some people have noticed a poorer quality in the recording, so you might want to try other ways if they are an option. Vocaroo requires no other software than a mic, because it's entirely online, so it's a fine place if you lack audio or video editing software.
If you need software to record with, Audacity is free to download and is of a good quality. It is also possible to make your own karaoke tracks with Audacity, as explained here. This is good if you want to record a song that you can't find instrumentals for.
If you can record audio directly into an MP3 on your computer, you might want to upload it to a file-sharing site such as 4shared.com or fileden.com, which both have the option of listening to recordings without downloading them.
singsnap.com and karaokeparty.com are two examples of sites to which offer online karaoke. Both are free, but require signup. And neither of them has the variety of youtube karaoke videos, although the quality is more closely monitored.
Alternately, you could post a video, with or without visuals, to youtube. The non-video sites have the benefit of no one seeing your Rachel Berry faces while you sing.

Recording Quality
Use the best recording service that is practical to you. Many people have found that uploading MP3s recorded on their computer is quite good.
Do not sing directly into your microphone. If your recording software has a little bar that goes from yellow to green to red, try to avoid going into the red. It creates feedback.
People in this thread have found that facing away from your computer is a good technique for not flooding the mic. It sounds strange, but it works.
You know how in videos of people in recording studios, they are listening to big, cushy headphones? If you can edit the background music in after you record, do this. It eliminates the background music, which will sound tinny after being played through your speakers and rerecorded.