Prior to the April 5th cycle, I had done loads of research on ISA accounts. Did a comparison from most of the major ISA providers in the UK and my opinion is that the ING ISA offered is the best.
Not only does it provide one of the highest (if not the highest) rates in industry, but you have the added advantage that interest is credited MONTHLY and calculated daily. If you withdraw money, you do not lose the interest for the month.
Most other providers may offer competitive rates, maybe even slightly higher rates, but don't credit you until the end of the year, which is useless.
So act now, you can be earning 6.55% for the next 6 months TAX FREE.
Have been with ING for about 1.5 years now, absolutely love them. Recommend them hands down.
You can open an ISA with as little as £1.
Feel free to post if you think there's a better deal, and I'll more than likely point out the flaws in it :)