TILES
Are very durable and best used above the hob and worktop where they will make a very efficient splashback.
They come in all shapes colours and sizes and their relatively high cost will be offset by long life and easy maintenance.
Work out carefully how many you need in your design so you can calculate the cost, and don't forget the adhesive and grout.
Most people fix tiles in between the wall units and worktops only as well as around the sink & hob areas. If you opt to tile from floor to ceiling all around the kitchen this will prove expensive. If you decide to give the kitchen a facelift in a few years by changing wall tiles you will need to take these all off again and this will probably involve plastering.
Grout can be matching or contrasting and can considerable enhance the appearance of the tiles.
You might also consider a row of decorative edging tiles.

PAINT
Is the quickest and cheapest way of decorating your walls and you do have a number of choices of finish (gloss, eggshell, matt) and a huge variety of colours.

WALLPAPER
Is a little more expensive than paint but comes in many patterns, textures and colours, which can enhance the appearance of you kitchen.
It is not advisable to hang wallpaper near to the hob or sink, as the increased volume of steam and heat in these areas will often lift the paper.
Good embossed wallpaper can look very like tiles and will also be extremely easy to clean
When choosing either paint or wallpaper, just be sure it is intended for use in kitchens and will stand up to the inevitable heat, moisture and grease.

STAINLESS STEEL OR BRUSHED ALUMINIUM.
Stainless steel sheets normally mounted on chipboard or sheets will act as a modern attractive and durable wall covering. The effect can be stunning. This option can involve considerable fitting work, as the sheets will have to be cut around obstructions such as sockets or pipe work.

LAMINATED SPLASHBACKS
Now very popular with modern & contemporary kitchen themes. Choose laminated sheets to match or contrast with your worksurfaces. Hygienic, easy to clean and attractive are just some of the benefits associated with this desirable finish.
Fitting method is similar to stainless steel, with the surfaces mounted on sheets of chipboard or mdf. 4mm mdf is recommended. Don't try and fit the thin laminate sheets directly on to the wall as they are very brittle and will almost always crack or split. Some manufactures will supply laminate sheets already mounted on sheets of mdf.

SOLID SURFACE OR SYNTHETIC
When choosing this type of worksurface consider following through with the surface on the walls. Granite, Corian & Christalite worktops are often complimented with matching splashbacks usually fitted to areas that would normally be covered with tiles i.e. between worktops and the underside of wall units as well as around the sink and hob area. This option is probably the ultimate in terms of style, looks and durability but will more inevitably be the most expensive

COLOURS
Your overall colour scheme will largely be a matter of your own personal taste but bright, contrasting colours often work best in kitchens.
Just imagine what brown units together with brown walls would look like!
You will probably spend a lot of time in your kitchen and you want this to be an enjoyable experience, not something that fills you with gloom and depression.
So, thought now = happy kitchens later