Updated list (15-Oct-2011) D Erikson says at the NYCC 2011 panel that ALL of the Flashpoints will be available to play at lvl 50 in a hard mode.
http://youtu.be/N9IGOEyrGK8 It's at about the 1m5s to 1m15s mark.
Quote
6:48: Q: How many of the 15 flashpoints are shared with both factions? A: Ohlen: About a dozen shared. Erickson: I do not remember end game count. Two plus endgame flashpoints.
15 Flashpoints (2 unknown FP's)
REPUBLIC
The Esseles - Early Game, Republic Only (lvl 8+)
Maelstrom Prison - Mid Game, Republic Only
Taral V - Mid Game, Republic Only (~lvl 30)
EMPIRE (Foundry and Boarding Party appear to be parts of the same winged Flashpoint)
The Black Talon - Early Game, Empire Only (lvl 8+)
The Foundry - Mid Game, Both Sides (lvl 32+)
Boarding Party - Mid Game, Empire Only (lvl 36+)
BOTH SIDES
Bringing Down the Hammer - Early Game, Both Sides (lvl 14-22)
The Tomb Opens - Early to Mid Game, Both Sides (lvl 17-24)
Directive 7 - Endgame, Both Sides
Battle for Ilium - Endgame, Both Sides
The False Emperor - Endgame, Both Sides
Lost Island - Data mined
Kaon Under Siege - Data Mined
???
???
2 Operations
The Eternity Vault
Hutt Operation
World Bosses - I'm going to guess about 13... Assuming that the noobworlds don't have these bosses, 17 if I'm proven wrong.