Cardiff is an amazing place to go shopping, You will find absolutely everything you will ever need, you have all the typical high street stores, New Look, H&M, Jane Norman all in the new St David centre, which also hosts every little gadget shop you can think of! But back to the clothes.. Queen Street is where Topshop (a massive THREE FLOORS!), Primark and River Island are found, along with Lipsy for pretty dresses for nights out and BHS and Marks for the older customer!
What I seem to love best about Cardiff though is the individual retailers, get lost in the castle arcade and you will find Eccentrix (one of the best shoe shops in town, very affordable) Hobo's (Vintage clothing at its best) an alternative fashion store underneath a fancy dress shop and two other shoe shops which are both still simply amazing. St Mary's street is where you will come across two more arcades both hosting some more amazing vintage clothing stores, along with skating stores and another alternative fashion store (Rebel Rebel)
If its charity shop's you are after The Oxfam Boutique (which sells some designer items) is on St Marys street and continue towards Cardiff Central train station for three other ones, all full of amazing clothes with good causes. If your looking for cheap fancy dress from a charity shop Scope (Churchill Way) always has something for me when I ask!

You will however need a lot of time and a lot of coffee and money to visit all these amazing stores!