I've been boycotting Amazon (UK) for a few years now. It's not easy! Sometimes it doesn't take much longer to source items, but other times it takes way longer. I have limits though, and occasionally I end up caving-in and just using Amazon, but it's getting rarer all the time. Now I use them once or twice per year. I tried using onbuy for a while, but we got a couple of faulty items from them and their support completely ignored me, so I stopped using them. Generally, here are some of my most common alternatives:

general stuff and gifts: Argos, ebay, etsy
tech: overclockers, ebuyer, scan.co.uk
electronics: John Lewis, AO, Richer Sounds
books/dvds: hive.co.uk, Waterstones, WH Smith
pharma: boots, simpleonlinepharmacy, well
household: Robert Dyas, Dunelm, John Lewis
pets: zooplus
spare parts: buyspares.co.uk

And for a wishlist alternative I use wishlist.com. (edited to fix formatting)