I would second most, if not all of the above, especially To The Ends of The Earth, If You Say Go, and Mission's Flame
4 suggestions of my own...
1. Multiply Your Love by Andy Park/Vineyard (on the CD "Change Me From the Inside")
2. Shout Your Fame by Hillsong London (excellent if you're looking for a more rock feel)
3. Here Am I, Lord by Dan Schutte... This is a modern hymn, and probably the best song on missions I've ever heard done for a worship context. There is an excellent version on this CD
if you can find it somewhere (or order it for only $3 on Amazon)
4. Where You Lead Me I Will Follow by Monique Tute/Vineyard... beautiful song... you can get it for free here