Most missionaries probably have someone Stateside that helps facilitate their finances. If you don't, or you want greater control or "situational awareness" of your financial situation you'll have to look at online banking
Mark Shead over at Productivity501 has a great list of 14 "must have" online banking features. I didn't realize banks offered some of these, like "online check images" or the ability to open accounts entirely through the web.
If you're shopping for a new bank, or aren't satisfied with your current bank check this out. Unfortunately, Mark declined to state where he banks (read the comments), so you'll have to use this post as a checklist.