My plan is only £50 - £100 per month put aside over a long term (18 years)
Definately recommend a invest based savings account with that length of time to save, saving on a regualr basis also a good way to reduce market volatility over the time your saving ' pound cost average'.
For deposit based savings, cash isa rates are not brilliant, but i think 3%+ can still be found, Santander, Halifax, Barclays were the best at the start of the tax year for rates, maybe not for service though.
Other savings accounts, ING have always been quite good at offering flexible savings with good rates.
The main thing to consider is what do you want form an account, access, return, limits etc... then compare the rate against inflation, to look at the 'real rate of return'.
Ie Inflation 5% if you get 3% on your savings after tax you still loosing the equivalent of 2% per year due to inflation cost.