Halfords aren't as bad as people make out, a "cheap" mountain bike (say in the £80-£200 bracket) isn't going to be any worse from Halfords than it would be from anywhere else. If you were looking for an expensive, specialist bike I would recommend going for more specialist retailers, but if you're looking for a basic, reliable towpath machine Halfords isn't a bad place to go, they do sell some cheap and nasty stuff, but I've seen nastier. A few things, as something of a bike buff, to look out for 1) Pay the little extra for alloy brake levers, the black plastic type are useless and usually a sign that other components may have been skimped on. 2) Don't be tempted by cheap bikes with rear suspension, they are heavy, hard to ride and prone to breaking, front suspension is a nice luxury (and some of the cheaper ones are very decent nowadays) but effective rear suspension is still pretty specialized and very expensive. 3) Personally I don't really rate disc brakes, they're good if say, you're hurling yourself down mountain sides at 30mph, or on motorbikes and tandems, but, although discs look cool, I'd take the tried and trusted "V" type rim brakes any day.
As for the web discount thing, just one of the crazy things about modern life I guess, I've done the same thing to get 10% from PC World before now.
Hope that's some help, if you wanna post a link to the bike you're thinking of buying I'll gladly have a look and tell you what I think.
. . . . also, if I remember rightly, Halfords have some kind of deal where you can pay around £30 a year for them to do all the servicing for you, could work out good value for some people.
