Tracks are widely available (and mostly very affordable) thanks to the wealth of karaoke and piano accompaniment tracks on iTunes. Try searching your song's title with 'karaoke', 'instrumental' or 'accompaniment' after it, and see what comes up! Sites such as parismusic.com offer brilliant quality backing tracks, though these do cost a little more. In my experience, voices do sound better over piano tracks, and it also matches what people will hear from you in an audition. Some songs, however, do need that big band/rock band backing to make them really sing.
Song choice is obviously very personal, and comes down to how you want your reel to sell you. If you're a very versatile singer, choose songs of different styles and genres to make sure that comes across. But, if you're a master of one style, then don't be afraid to play to your strengths - there's no point showing any weaknesses!
Also, pick songs that sit well within your range, and make sure the tracks match the key you want. Too many people try to sing something too high, and end up highlighting weaker parts of their voice.
WHEN WILL I GET MY REEL?
You should receive your tracks within 5 days of the recording session, but please allow up to a week. You will, however, be kept informed all along the way!
WHERE ARE YOU?
I'm now based in Sydenham, a very (very) short walk from Sydenham Overground Station (orange line).