In the UK you can put up to £11,520 per year into an Individual Savings Account (ISA). This account allows you to invest in stock, unit trusts, index funds etc. and all income and capital gains are free of tax.
Crucially, there is no requirement for this investment to be used for retirement and there is no penalty for withdrawal.
I view this as quite an efficient short/medium term saving mechanism. It also puts your money away in a place that makes it slightly harder to get at (have to sell your investments to get the money out etc) so you aren't tempted to use it in the short term.
Is there any equivalent in the US? IRA is basically the same thing, but of course this has penalties for withdrawal before retirement.