I have been looking into this over the past few days. The cheapest prices I have found are £150 for the 6600gt, £140 for the 6800le and £120 for an ex demo 9800pro (all agp).
Out of all of these the 6600gt is the best performer at stock settings and I reckon that it could be overclocked ~10% too. The 6800le is probably the same speed as the 9800pro but of course there is the chance to softmod it to be a 6800gt or np. Is that chance worth the risk and an extra £20? I am not so sure as I picked up a 256bit 9800se as my last card which, I softmodded to a 9800pro. It showed artifacts in dx9 tests but was flawless in unreal tournament 2004. However it died.
So a choice between a 9800pro and a 6600gt. Is the extra £30 worth it in the long haul? I think it is because of the extra fillrate as, fillrate = performance . The memory also seems to be conservatively clocked too so that can aleviate the bandwidth concerns. Then of course there is the sm3 feature set.
Of course everyone is going to have their own opinions on this subject but could it be that the 9700pro at £95 is the best bargain of them all?