Ramadhan the fasting month

When beginning the fast- Suhur
Wa bisawmi ghadinn nawaiytu min shahri ramadan

I intend to keep the fast for tomorrow in the month of Ramadan
[abu Dawud]

When breaking the fast- IftarAllahumma inni laka sumtu wa bika aamantu [wa 'alayka tawakkaltu] wa ‘ala rizq-ika aftarthu

O Allah! I fasted for You and I believe in You [and I put my trust in You] and I break
my fast with Your sustenance
["wa 'alayka tawakkaltu" is quoted in some books of knowledge - but not all, hence it is in brackets]
[abu Dawud]

dhahabadh-dhama’u wab-tallatil ‘urūūqi, wa thabatal arju inshaAllah

The thrist is gone, the veins are moistened and the reward is confirmed, if Allah [Ta'ala] Wills
[abu Dawud 2:306]
Upon breaking the fast in someone’s home

Aftara ‘indakumus saa’imuna, wa akala ta’aamakumul-abraaru, wasallat ‘alaikumul mala’ikat
May those who are fasting break their fast in your home, and may the dutiful and pious eat your food and may the angels send prayers upon you.
[abu Dawud 3:367, ibn Majah 1:556, an Nasa'i]

http://www.geocities.com/mutmainaa/dua1/Ramadan_dua.html