There are loads of sites where you can find good accessories online which cater to all kinds of tastes. I'll link you to some of the sites I like to use and give a quick summary of the sort of thing they sell.
Claire's has a large range of accessories, for low prices. They don't carry much 'high-end' jewellery, but they have some colourful and fun stuff for when you're on a budget. They also often have sales, so the accessories get mega cheap!
Shop Jeen has an absolutely huge range of accessories. They really have something for everyone and always have a large selection of very on point stuff. The price range is pretty big so it doesn't matter so much how much money you want to spend, there'll be something. Definitely one of my favourites.
Etsy and Big Cartel
If you're looking for something a little different which you're less likely to see someone else wearing, Etsy is the best place. It's the home of home-made and vintage products, with loads of jewellery. You can search for anything!
Big Cartel is a similar service, with artists, jewellers and clothing brands selling their stuff by themselves, which usually translates to savings and more unique purchases for you. One of my favourites is Lunar Made, great for crystals and on trend accessories:
I hope I've helped and if you can't find something, it's always worth trying eBay, or checking out your favourite clothing shop's site and looking at the jewellery section. Topshop and Urban Outfitters have some cool stuff.