I am a big fan of Abercrombie & Fitch (don't laugh; I know they're not edgy, but I really love their knitted tops-- they go so well with H shawls worn around the neck in winter!), H&M, Zara and Karen Millen, along with some more high-end labels like Alexander McQueen, See by Chloe and Armani Collection. Marni is a bit too out there for me, but then I tend to buy my staples or long-term statement pieces from the high-end labels and then supplement them with frequent purchases from the high street labels which can easily be donated or recycled when they date or become unwearable (some things are really of dire quality).
Honestly, I love to wear my H bags with a mix of high street and designer, and then to add on H accessories-- scarves and especially shawls, as well as little bits of jewellery here and there. Something as simple as a CDC and a shawl can make a big difference to an outfit and take it from toally boring to totally chic in the blink of an eye, IMO! And like India said above, a good haircut that can be styled a number of different ways makes a huge difference-- something I have only just learned in the last month or so!