Cash gifts would be the norm among our circle, as most couples would be either renting together or have already bought a house together and asuch would not need the usual toaster/sheets/saucepan sets that couples years ago would have appreciated when setting up home together.
Depending on how close we are to the B&G, the scale for us goes from 100 (between us as a couple) for say, attending an afters of an acquaintence, to approx 300 for close friends.
When we got married ourselves 2 years ago, most people gave cash as gifts, as we had been living together for 3 years previously and were not in need of the usual household gifts. We did of course get the odd gift of waterford crystal bride and groom statuettes (now unfortunately gathering dust in their boxes due to DH's allergic reaction to ornaments of any kind) and massive serving platters or ornate photo frames from the older family members, but which were appreciated as very thoughtful. Cash gifts ranged from 50 to 250 depending on how close the people were to us.
DJkat - my DH was best man at a wedding recently and we gave approx 300 as a cash gift, along with helping in the runup to the event with organising the event itself.
I would find it the height of rudeness to specify what gifts you expect on the day - be that a wedding gift list with a store like BTs or specifying cash gifts only. IMHO the B&G should be happy with people turning up on the day itself to celebrate the event and not be totting up the amount various guests will be contributing to covering the cost of the meal etc. We had a few people turn up to our wedding who didn't give a card let alone a gift but we were delighted they made the effort to turn up on the day at cost to themselves (time off work, travel, outfits etc) and at this stage I honestly can't remember the specifics of who gave what, only that we were happy so many people turned up to give their good wishes.
Personal circumstances dictate how much people can give - eg a student giving 50 euros when they are obviously broke and scraping their rent together each week meant as much - if not more - to us as say 5 times that amount from family members, as it was clear the 50 euros was an awful lot to get together for the person in question, never mind the cost of attending the day in itself.