The biggest Electricity company in Spain is Endesa - from their webpage you can request an electricty or gas connection, and check your account status (as long as you speak Spanish). For those who are yet to move to Spain, prices are similar to those in the UK.

Gas

Mains gas is not available in all areas. If it is available in your area, look at the Endesa site above, or look in the Yellow Pages to find your local gas company. If it is not available then you will be able to get bottled gas - again, look in the Yellow Pages.

Telephone

The biggest telephone company is Telefonica and you will need to contact them to gat a phone line connected. Once you have a phone line, however, there are a number of companies who offer cheaper rates on all calls, including International calls:

Auna (site in Spanish)
An easy-to-use service which can be "pre-assigned" (i.e. they switch a button and all of your calls will be through them)

Gotel (site in English)
A pre-pay service (so no messing about!) offering cheap international calls