DH has a Logitech M215 and says it's fine. He's a heavy user and the batteries last him 6-8weeks. The only thing is that he thinks it's less accurate than his conventional wired mouse and it jumps slightly which can be annoying but it's obviously not that annoying because he's been using it happily for months.
Thank you ladies. I will have a look into the mice that you've suggested. I'm actually considering a mouse with a recharging station, so then I'll not need to worry too much about batteries etc. Daisy, is your Microsoft mouse rechargeable? there was a similar Microsoft mouse (Microsoft BlueTrack Explorer Wireless Mouse ) which is similar I think and seems to be rechargeable :-) Most of the others appear to be really expensive