use cheap airlines within asia to hop to different countries. asian ryanair equiv's. e.g. tiger air.
As to previous post, some people love singapore (i loved it and went back 4 times), others find it bland.
it has amazing food. great spot.
siem riep in cambodia is good. one day was enough for me though. you can buy week, 3day, 1day tickets. i bought 3day and gave it away after 1day. its a must though.
again, stay away from indonesia (7 of 8 of our group brought their tickets forward to leave early. it's hell-and all of us had knocked about alot).