Seems like everyone is recommending what they have rather than what is needed. Maybe one of these:
http://www.tantronics.co.uk/acatalog..._Charger2.html
1-14 cells NiMh and NiCad
1-5 LiPo
Will also charger 12v lead-acid batteries
12v and mains power input
Doesn't appear to cycle but it's inexpensive so won't loose much on resale.
Never used one so I don't know how good they are.
If you go down the second hand route, you can get some good race spec chargers from LRP, Novak, orion, etc for around £50 but then you will need a mains-12v power supply and a 12v lead-acid charger.