for a dyson. if you dont wana spend too much, dont have asthma and dont need to worry about space then the dc19Y. if you wana pick up pet hair then chuck on a turbo head with this and your set.
if you want something better, want cleaner air and want it to come with a turbine head (a must for pet hair on carpet then get the DC23 turbine head. few extra little features + its a newer model so a bit different but better design.
if you want a upright then the dc25 (i think) is good...light, easy to push around + a power head........plus its purple.
bit hard to explain when im not in the shop...but they are the three i would go for.