Make sure you use your ISA allowance, in fact you could get your �3500 now and then out the balance in a fixed term deposit until March and then put the remainder in April into another ISA.
How long is it spare for ? If it's 10+ years, put it in the stock market (if you're new to this, use unit trusts). Otherwise building society (cash ISA if you haven't got one for this year). And if it's totally spare, pension!