You might want to narrow this down. Designer bags can range from £150 to £3,000+ depending on the brand, or if you want the Birkin bag £10,000+!!!
I love Polene bags, for me they sit at the right price point (£300-£500), are really well made, have a number of beautiful designs, and leather colours and finishes. I particularly like the Un Nano, and Sept.
A bag I have lusted over for a really long time is Gucci Dionysus in tan suede, to me it is beautiful, but more than I am prepared to pay for a bag, and the tan suede concerns me in terms of longevity.
Chloé Drew is a really pretty ladylike bag, the deign has been popular for over 5 years and I still think it is stunning. Again, over £1,000, so I would not buy it at a new full price, though I would consider a secondhand one. Chloé also have other styles which are really pretty such as Faye and Tess.
Givenchy Antigona is really lovely, whenever I see it I think how beautiful and classy it is but still has some intriguing features.
Chanel bags are really popular - to me they are a little too traditional and dull and I don't love them, but they are popular for a reason. Very expensive, but if you buy a Boy in caviar leather they supposedly keep or even go up in value. Just a warning I have seen people saying that they think Chanels newer bags are lower in quality?