First of all: if you have a BATF license such as was mentioned in an earlier post, you can buy commercial e-matches for about $.25 each.
If not, 32ga nichrome wire is accepted practice, about 3-4 inches at most. You can also go buy model rocket ignitors from Wal-Mart. If you want the best, most reliable option, make your own e-matches from a kit. Skylighter.com sells the chips & compound (pyrogen) to make your own... nearly as good as commercial & cost just a few pennies each. They only require about 200mA @12VDC, but standard practice is to design for .5A for a single e-match; .9A for e-matches in series.
For my shows (I'm a licensed pyrotechnician), I use a pair of 6v lantern batteries in series. They've worked reliably for years. I just use a meter to short the terminals. If I get 2 or more amps, I'm good to go. I get them at Wal-Mart for $4/pair.