In reply to Denni:
When you say a couple presumably your meaning that your looking for the small (cheap) ones? Depending on what the problem actually is, you could well be just wasting money on these ones as they mainly limited in their extraction rate/amount and meant for very small rooms/cupboards.
Do you know why you have condensation? Single glazing, lack of heating, lack of insulation, lack of ventilation, lack of extractor fans, etc? Also how much water are you needing to extract? All this will dictate what size of machine if one is needed. No point in a dehumidifier if the cause of the condensation should be address by other "solutions".
Anyway, I've used ebac machines
http://www.ebac.com for over twenty years (well only actually two machines in that time with the current one, a 2650e, still going strong after eight years). Not cheap to buy, but effective and long lasting. I did experiment with cheapie small ones a couple of times and they failed to have any real effect.
Originally bought one as the then house was a bit damp overall and it ran permanently on for 6 years. Thereafter with subsequent houses I only use it for removing the excess water generated by washing and drying clothes and occasionally to lower the humidity level in the whole house (this year with the summer we've had the overall humidity is higher than it would normally be and the dehumidifier means I can run the heating lower and still keep the house drier).