There are a huge amount of types and styles of bulbs available these days.
They will generally all be 230 volts with the exception of low voltage bulbs found in some down lighters which, for instance, which will be 12 volts.

The power of the bulb (which will determines how bright it is) will be determined by the wattage which will vary. E.g. for standard light bulbs(230volts 40 watts will be dim), or, (230volts 150 watts will be bright).

Take care that you aren't buying too powerful a bulb as some light fittings will stipulate a Maximum Wattage, often Max. 60watts. This is usually because bulbs generate heat and too powerful a bulb may damage the light fitting.

Energy saving bulbs use much less power than normal bulbs so save you money and help reduce CO2 emissions. So they are still 230volts but the wattage will be much lower for the same amount of brightness.

E.g. a 20watt energy saving bulb is roughly the equivalent of 100watt standard bulb which uses 5 times the power!!!

Low energy bulbs are mini fluorescent tube type bulbs. They are currently being superceded by LED bulbs. Most can't be used with a dimmer switch though some LED's can be. Some people don't like the colour of these bulbs
The closest match to traditional bulbs are "warm white" ones

There is a huge choice of styles and types or fittings. The fitting will type will have a code. A traditional british standard fitting is bc (=bayonet cap)

Come in various lengths and thickness depending on the size of you fitting. The longer the tube the more light it gives and the greater the wattage. These are low energy to.

Fluorescent tubes also need a clip in "starter" to make them work. Try replacing this if you've tried the tube(they twist and lock). They are supplied in different ratings to match the tube wattage.

Dichromic bulbs used in down lighters. Come in a variety of wattages and angle of beam (eg from narrow spot light to wide beam).
Two types are available for use in different fittings

12volt GU5 push fit pin fitting
230 volt GU10 fitting (twist to lock)

Energy saving bulbs come in several styles. The most common fittings are BC and ES

Checkout http://www.lightbulbs-direct.com which supply a huge range of bulbs at great prices. Their bulb finder section, glossary, and fitting types is very useful.

Tip Test bulbs with a continuity tester. ( NB you can't test fluorescent or low energy bulbs like this)