I managed to find this deal online whilst looking for the Samsung Galaxy S for free on an 18 month contract. Seems to be the best deal I can find so far.
You can get the Samsung Galaxy S for free on a £20 a month (18 month) contract from Dial-A-Phone.
I assume its the 8GB version as it doesnt say otherwise.
Note: This deal is intended for those of you (like me) who are looking at a cheap way of purchasing this phone (by paying installments). You can ditch the simcard provided (or pass it onto a family member) and use your current contract sim.
With the added £40 from Quidco it can potentially bring the overall cost down to £275.