Our bank (Lloyds) allows you to transfer £25k at a time simply by using your debit card (which is a bit scary when you think about it).
The rate's still not brilliant (£1: 1.11Euro) but it's better than it has been and the transactions are free.
When you apply for your NIE number (which you need to become a Spanish resident) you can then open a Spanish bank account.
Th only problem is, we have discovered that you need to go into your branch to set up internet banking for some bizarre reason, so transferring money was initially a bit of a leap of faith which resulted in a few sleepless nights.
All in all it's quite a simple process and we're now getting a better return on the money which had previously been accruing almost nothing for the last 10 years in our ISA's.