For the tax year 2010/2011 you are allowed to invest as much as £5,100 in a tax free cash ISA. Halifax are a popular choice for ISAs with many people so below you can find the cash ISAs they have available as @16/02/2010. They also allow you too transfer your ISAs to them.

ACCOUNT	INTEREST RATE	MINIMUM INVESTMENT	MORE INFORMATION
ISA DIRECT REWARD	2.80%	£1	Unlimited withdrawals during the 12 month reward period. No notice required. Minimum withdrawal £10. If your account balance falls below £1 the ISA Saver Direct variable interest rate and account conditions apply to your account from that date. After the 12 month reward period, the ISA Saver Direct variable interest rate and conditions apply.
Variable Rate ISA Saver	FROM 0.1%	£1	Variable interest means the rate you earn can go up or down.
1 Year Fixed Rate ISA	2.00%	£500	No withdrawals allowed. You can close your account at any time but you will lose 180 days interest.
2 year Fixed Rate ISA	3.50%	£500	No withdrawals allowed. You can close your account at any time but you will lose 180 days interest.
3 Year Fixed Rate ISA	3.55%	£500	No withdrawals allowed. You can close your account at any time but you will lose 180 days interest.