Metal Suppliers
If you need more than a tiny amount of metal, you're probably best off working with a local supplier:
Westbrook Metals - Large supplier of metals near ASMBLY. Offers cutting services, but not necessarily while-you-wait. Has the best drops section in town; bring cash and you might get a deal.
Metals4u - Round Rock location run by the same folks as Westbrook. Their drops section usually only has aluminum.
Asero - Only sells steel, but their cut time is quick and pricing is quite competitive.
South Austin Metals- Sells steel and aluminum, and can often get special orders next-day. Cuts while you wait.
In a pinch, you can order online:
Online Metals makes custom cuts and ships from Dallas.
McMaster-Carr is a great source for hardware and off-the-shelf random bits of metal.