Trevor has made a good point, diversify. Its more than likely a good idea to have lots of smaller investments rather than putting all your eggs in one basket.
Heres a few ideas
1. Isa's are almost certainly a must, its probably the only one thats 100% guaranteed. (other than a savings account which you will be taxed on) So fill your ISA's before your savings account and make sure you keep an eye on the interest rate you are getting on the isa, if its not a competitive rate move it
2. Property. As already mentioned if you can afford to get a buy to let, it might be a good investment (but you will almost certainly need to pay tax on these) Or buy a big expensive house now and then downsize (this way you avoid capital gains tax etc)
3. Stock markets, gold, silver etc. Prices can rise alot but they could go down as well. Some make an awful lot of money out of it, most it seems, do not.
4. Sell or rent your business, the latter could provide you with a good steady income for a very long time
5. State Pension. Dont forget you will get this, if have no other income it will be at least £130 a week.
5. Retire abroad, somewhere where the cost of living is cheaper, that way you will not need such a big pension, not suitable for everyone but it will be for a few, me included!