In reply to robw007:
I've just sold my property in Spain. It took a year, but at the end went really quickly, just over a month from offer to completion. I was very lucky - some of my neighbours have had their properties on for several years now, always chasing the market down and being above the value rather than below it.
You can use as many agents as you like, but watch the small print of their contract. Some claim sole selling rights which means you still have to pay them commission even if another agent sells it, most however are fine so far as this is concerned - but do check!
As has been said commission rates are much higher than in the UK. Look for pro-active agents. Most are useless and just list the property and sit on it. Most are not very good at valuing either and just tell you what they think you want to hear, which is usually too much.
Make certain that all your legal work is in order - the agent will need to see all this and copy it. Most agents won't touch "illegal" builds. They will also need to see up to date water and electricity accounts.
Depending on when you bought expect to take a huge hit on the price. I bought at the height of the boom in 2005 and lost just under 50% on what I paid. It was painful, but I think the situation is getting worse as more and more aging ex pats flood the market in Spain's struggling economy, and prices have continued to fall since I sold. You need to substantially undercut the prices being asked by other similar property to have any chance of selling.
The agent draws up the contract and takes the 10% deposit which they pay into your account, first deducting their commission from it, before completion!!
Be prepared to have a percentage of the purchase price withheld back by your solicitor against outstanding taxes, including rubbish tax, non-resident tax and capital gains tax. It can take up to 4/5 years before the Spanish tax office agree for this to be paid to you. Too many ex pats have left the country owing tax.
Good luck