Many bargains to be had in the fragrance department 'Pour Femme' et 'Pour Homme'... Many of the larger sizes beat the smaller sizes for price/value. For example, Paul Smith Rose EDP 100 ml is £16.66 whereas the 50ml is £25, and Calvin Klein Euphoria EDP 100ml is £32.99 but the 50ml is £34.05.

All the fragrances and prices I've listed are sold by and dispatched by Amazon. Not third party sellers.

Here are some highlights and a price comparison below - you'll see that some cost double at other retailers (eg Boots, Superdrug). Click on the fragrance name to visit the page directly. You can browse all available products using THIS LINK
(That's set with the filter at 70% off - change if you like.)

Feel free to add suggestions to put in the post if the deals are eye-poppingly good.

Paul Smith Rose Eau de Parfum for Women - 100 ml £16.66 (was £22, and is £13.34 cheaper than 30ml!)
Good value VS 30ml is £30, 50ml is £25.
(Next cheapest is £20 Asda, £24.95 Fragrance Direct, £28.50 Boots)

Calvin Klein Euphoria Eau de Parfum for Women - 100 ml £32.99
Good value VS it's just £1.06 more than 50ml! (£34.05), and elsewhere it costs £38 (The Perfume Shop), £45 (AllBeauty), £70 at Boots and The Fragrance Shop!

Calvin Klein Eternity Moment Eau de Parfum for Women - 100 ml £18
Good value VS it costs £34 (Boots), £20 at The Perfume Shop, and £56 at Superdrug!

Sarah Jessica Parker Lovely Eau de Parfum for Women - 100ml £14.99 (RRP £49.99)
It's a deal because: it's just £5 more for 70ml extra compared to 30ml is £9.95, 50ml is £16.44. Good value for 100ml!
(It costs more elsewhere, but it is £14.99 at Argos.)

Joop Homme Eau de Toilette - 125 ml £18.79
It's a deal because: it costs £23-£25 elsewhere (Boots, Superdrug etc) AND Amazon is selling £16.39 for 75ml. However, a good buy is 200ml for £25.53

Calvin Klein Obsession Femme Eau de Parfum - 100 ml £20
It's a deal because: it's much better value than prices/sizes elsewhere, for example 50ml is £16.95 from AllBeauty and it generally costs more. It's worth noting that 100ml is £24.99 Boots.

Hugo Boss Bottled Eau de Toilette for Men - 200 ml £46.99
It costs £43.90 for 100ml versus £76 at Boots and £76.50 at The Fragrance Shop! It was £56 at John Lewis but is OOS, and 50ml is £45 at The Perfume Shop

Issey Miyake L'Eau d'Issey Vaporisateur Natural Spray EDT for Women - 100ml £45.77
It's a deal because: it costs £75 at John Lewis!, or 50 ml £29.99 vs £40 at Tesco, £60 at Boots

Ghost Women's Sweetheart Eau de Toilette Spray - 50ml £17
It's a deal because: it costs £25 at Boots, £28 at Superdrug, £33.50 at The Fragrance Shop

Jean Paul Gaultier Classique Eau de Toilette for Women - 50 ml £29.99
It's a deal because: it costs £53 Superdrug, £51 Boots, £42 AllBeauty

Beyonce Midnight Heat Eau de Parfum - 100 ml £8.99
It's a deal because: it costs £11.45 at allbeauty.com, £10.99 Groupon, £19.25 Boots, £12.99 Fragrance Direct, and 50ml costs more at £10.90.

The discount link is for the offer Amazon is advertising (promotion page is here).

Be careful to only buy where Amazon.co.uk is the seller - this link with up to 70% off: https://www.amazon.co.uk/s/ref=lp_4222010031_nr_p_6_0?fst=as%3Aoff&rh=n%3A117332031%2Cn%3A%21425565031%2Cn%3A%21425567031%2Cn%3A4222010031%2Cp_6%3AA3P5ROKL5A1OLE&bbn=4222010031&ie=UTF8&qid=1482164253&rnid=122947031

If you want to apply your own discount level to see other fragrances, you can use the filter tool on the MoneySavingExpert website to pick a discount level/range in the department and sub-category you want.