Formal/prom dresses - If you choose the right time of year to shop, there are plenty of pretty dresses available in gorgeous styles and colours for girls going to their end of year proms.
Different dresses - If you bridesmaids come in different shapes and sizes, consider getting a completely different dress (style, colour or both) for each bridesmaid. Just remember to vet them before the big day!
Bridesmaid/groomsmen pays - Remember that it's customary for the bridesmaid and groomsmen to pay for their own dress/suit and shoes so make sure you enforce this.
Suits - Try to buy the grooms suit. You'll find that it's only a little bit more and if there's any accidents you know you won't have to shell out for drycleaning straight away. Hiring suits can often cost as much or more than buying one.
Bridal dress - Consider buying a second hand dress. You can get fashionable and barely used dresses for a fraction of the cost. If they aren't exactly what you want, you can get them altered.