As a woman, you should be fine with わたし in most cases, but if you're curious, there's quite a lot of them actually. わたし - the most common and versatile, not always suitable for males though; ぼく - used by males, especially juvenile ones; おれ - males use it in informal situations when speaking to friends; わたくし - more polite version of わたし あたし - informal, cute version of わたし, only for females; わし - samurai used it, these days it only appears in manga and TV; おのれ - another archaic word; うち - literally means "inside", but it is often used as "I/we/my family", (AFAIK, especially by women); and so on... http://nihonshock.com/2009/11/the-many-ways-to-say-i/

My best advice is to stick with WATASHI as long as you can. It my opinion, it is the only one you need, especially in a professional environment. However, here is another that hasn't been mentioned yet, just for kicks. われ - Old-fashioned way of expressing "I" (oneself). src: http://ejje.weblio.jp/content/%E6%88%91