If you are really unfit, The Little Black Dress work out by Zoe Lucker is actually very good. It has a warm up, dance, kickboxing, tone and yoga type sections, each lasting 10-15 minutes. You can mix and match as you please. Its a good one to get started with, imo.
If you want something more challenging, Davina MaCall's Power of 3 is excellent. It is divided into 3x30 minutes section, The Pump (with weights), Cardio (kickboxing mainly) and Core Stability (yogaesque).
If you really want to go for it, Billy Blank's Tae Bo is brilliant. He has several DVDs. I bought Get Ripped recently. The first part is like a training section to help you pick up the moves and do it properly. The middle part has has an eight minute intense cardio section for those who are pushed for time. Trouble is, according to my clock, it goes on for about 20 minutes . The last workout is a typical high energy Billy Blank workout. What amuses me about this one, is that there is a boy of about 7 years of age there and he looks completely disinterested. What is that all about?
If you like to dance, the original Pump it Pp by the Ministry of Sound is simply superb. It is very energetic and gets even more energetic when you do the High Energy section. Only do this if you are not easily demoralised and are quite coordinated.
Good luck!