Hmm. Some brief (and perhaps in some cases harsh) assessments from my memory...
If you have a set of very rose-tinted spectacles, Slough still wouldn't qualify as attractive under any circumstances, really. (Feels less of a shantytown than Basildon, maybe)
I can't think of Waltham Cross (for all that it has its own Charing Cross) as anything other than a complete dump. Waltham Abbey is not much better IMHO. And as for Dartford...well you can see a school named after Mick Jagger there. Nuff said I fear. Watford or Borehamwood both leave me cold, although I'd be hard pressed to decide which of the two is the more unpleasant. St Albans is a genuinely nice and interesting town, but alas the red bus there isn't oysterable.
Debden is a complete dive. Loughton has a few historic buildings, but is utterly devoid of culture and good taste, and while it's convenient for Epping Forest (and specific bits thereof like High Beach), maybe Chingford is a better starting point. And I'm not sure that "Birds of a Feather" was wide of the mark in its illustration of Chigwell...
Staines is better than people who don't know it generally think it is, but really the best thing about it is that it is on the Thames, with some agreeable walks to other places. Potters Bar is, more or less, similar (dull suburban overspill town), but without the advantage of the river.
Brentwood is not entirely without charm (it has quite an interesting, elegant, (Catholic) cathedral that no-one from outside the town seems to be very aware of, and which, from the outside, you probably wouldn't immediately suspect had only been built 20 years ago); the town itself isn't unpleasant, either - there are a few historic things to see in the town centre and thereabouts. Definitely an increasingly "millionaire footballer" and "footballers' wife" feel about the town, though... (mind you, if you really want somewhere blingtastic just over the boundary into Essex, Buckhurst Hill is the place to go)
A village rather than a town, but Tatsfield (end of the 464 route from New Addington) is a lovely place, and a good base for walking into the North Downs too. Much nicer than Passingford Bridge, the other out-of-zones village terminus, where there is really next to nothing to see at all (the M25 maybe). The out-of-zones villages on Tfl bus routes in Thurrock (South Ockendon, Aveley) are rather charmless and unremarkable too - both of them are dominated by mini-housing estates essentially transplanted from London.
I've never been to Redhill or Westerham, although I'd wager the latter, at least, might have some pleasant things to be said about it.
