Yes, you will be able to put your Standard Life shares into an EQUITY ISA, but only if you asked for a share certificate at the time you received them, rather than them being held in a nominee account. This could be a self-select ISA, or I believe Hargreaves Lansdown, financial advisers will accept them. However, bear in mind that a single holding in one company is always more riskier than holding unit trusts where you investment is pooled over the shares of many companies and therefore the risk is reduced.
Or, you can sell your shares and put the money in a Cash ISA up to a limit of �3000 each tax year.
Just remember that if you received free shares in the recent float, it may be advisable to hang onto them until after the end of July 2007 as they will be issuing additional free shares to everybody who is still hold their existing shares.