A 3D map I saw on the web (click to enlarge):

Both are recommended by backpackers:

http://www.jasminelodge.com
http://www.rosyguesthouse.com

Cheapest of 'em ol:
http://www.yellow-guesthouse.com/room_rates.html

Nov 11, 2009 Wednesday: Arrival from Manila to HCMC; PM: Saigon City Tour
Nov 12, 2009 Thursday: HCMC to SR (12hrs)
Nov 13, 2009 Friday: Angkor Day
Nov 14, 2009 Saturday: Angkor Day
Nov 15, 2009 Sunday: Back to PP
Nov 16, 2009 Monday: Back to HCMC (12hrs)
Nov 17, 2009 Tuesday: Mekong or CuChi Tour
Nov 18, 2009 Wednesday: AM: Saigon City Tour Departure: HCMC-Manila
-Edited. I had wrong dates on the original.