Does a character who is prone lose his Dex bonus to AC? It seems logical he would considering his restricted movement, but I can't find anything about it in the PHB or DMG. ANy help would be appreciated. Thanks!
Were that rule anywhere, it would appear on Table 8-8 on page 132 of the PH. You'll notice that right below the line 'Defender Prone' (showing a +4 for melee attackers and a -4 for ranged attacks), the entries for 'Defender Stunned' (and several following entries) have a 'cross' asterisk. This refers to the line indicating that 'the defender loses any Dexterity bonus to AC'.
Prone defenders continue to receive a Dex bonus to their AC. Q.E.D. Rolling around, I guess.
Christian is correct. Prone guys still retain their dex bonus (if any) to AC. Of course, melee opponents still get +4 to their attack rolls against them.