Most commercially grown flowers will last at least a week if you care for them properly.  Here's a few basic steps you can follow to get extra life and pleasure from your flowers:

Conditioning: a term florists use to mean getting the flowers ready for arranging - use this proven step-by-step guide to to ensure that your flowers last longer and look lovelier:

1. Make sure vases are very clean - bacteria kills flowers

2. Use fresh lukewarm water with commercial cut flower food added - the only exception is spring bulb flowers - they prefer cold water.

3. Strip all leaves below the water level - rotting leaves causes bacteria which kills flowers

4. Take at least 3cm (1") off all stems, making a slanted cut with a sharp knife or very sharp scissors - this creates a bigger area to take up water.

5. Avoid direct sunlight, heat, or draughts which can shorten flowers lives.

6. Keep flowers away from fruit and remove faded flowers as they occur.

7. Top up the water regularly and add flower food in proportion.

In general, white and pale flowers are particularly strongly scented, eg oriental lilies, tuberose, tazetta narcissi. Freesia are an exception to this - darker red and pink varieties have the strongest scent.

Bear in mind that a cool room is better for prolonging the life of cut flowers; but too cool a room may prevent scented flowers giving off their full perfume.

Spicy/Peppery

Ivy

Chrysanthemum

Florists' broom (Genista)

Hypericum - spicy

Pink (Dianthus) - sweet clove

Stock (Matthiola)

 

Sweet/Floral

Ivy

Bouvardia

Carnation - especially "Bagatel" (white spray), "Gipsy", "Candy White"

Freesia - especially "Aladin" (yellow), "Blue Moon" (lilac), "Cote D'Azur" (purple), "Golden Wave" (rich yellow), "Oberon" (burnt orange), "White Wings" (white)

Hyacinth

Lilac (Syringa)

Lily of the valley (Convallaria)

Phlox

Rose - especially "Extase" (rich purple-red), "Jacaranda" (deep blue-pink), Juliet (soft apricot), Rosalind (pale pink)

Sweet pea

 

Citrus

Ivy

Mimosa (Acacia)

Waxflower (Chamelaucium) - lemon and marzipan scent

Eucharis - delicate lemon curd scent

 

Aromatic

Ivy

Dill (Anethum graveolens) - aniseed fragrance

Eucalyptus foliage - rub the leaves for the full effect - medicinal rub

Lavender foliage - herb sachets

Marjoram - italian dinners

Matricaria (Tanacetum)

Grape hyacinth (Muscari) - faint musk

Rosemary foliage - sunday lunch

Heavy / Exotic

Ivy

Gardenia

Oriental lily - especially "Casablanca" (pure white), "Le Reve" (pale pink), "Stargazer" (white with dark pink stripe), "Pompeii" (white with yellow stripe)

Longiflorum lily

Narcissus - especially "Cheerfulness" (double lemon), "Paperwhite" (pure white), "Soleil d'Or" (golden yellow), "Ziva" (pure white)

Stephanotis

Tuberose (Polianthes)