Below is a list of values for the Msg parameter of PostMessage and SendMessage. To discover more about how to use a particular message (e.g. WM_VSCROLL), look it up at http://msdn.microsoft.com or with a search engine of your choice. Also, check out the Message Tutorial.
0x00 WM_NULL 0x01 WM_CREATE 0x02 WM_DESTROY 0x03 WM_MOVE 0x05 WM_SIZE 0x06 WM_ACTIVATE 0x07 WM_SETFOCUS 0x08 WM_KILLFOCUS 0x0A WM_ENABLE 0x0B WM_SETREDRAW 0x0C WM_SETTEXT 0x0D WM_GETTEXT 0x0E WM_GETTEXTLENGTH 0x0F WM_PAINT 0x10 WM_CLOSE 0x11 WM_QUERYENDSESSION 0x12 WM_QUIT 0x13 WM_QUERYOPEN 0x14 WM_ERASEBKGND 0x15 WM_SYSCOLORCHANGE 0x16 WM_ENDSESSION 0x17 WM_SYSTEMERROR 0x18 WM_SHOWWINDOW 0x19 WM_CTLCOLOR 0x1A WM_WININICHANGE 0x1A WM_SETTINGCHANGE 0x1B WM_DEVMODECHANGE 0x1C WM_ACTIVATEAPP 0x1D WM_FONTCHANGE 0x1E WM_TIMECHANGE 0x1F WM_CANCELMODE 0x20 WM_SETCURSOR 0x21 WM_MOUSEACTIVATE 0x22 WM_CHILDACTIVATE 0x23 WM_QUEUESYNC 0x24 WM_GETMINMAXINFO 0x26 WM_PAINTICON 0x27 WM_ICONERASEBKGND 0x28 WM_NEXTDLGCTL 0x2A WM_SPOOLERSTATUS 0x2B WM_DRAWITEM 0x2C WM_MEASUREITEM 0x2D WM_DELETEITEM 0x2E WM_VKEYTOITEM 0x2F WM_CHARTOITEM 0x30 WM_SETFONT 0x31 WM_GETFONT 0x32 WM_SETHOTKEY 0x33 WM_GETHOTKEY 0x37 WM_QUERYDRAGICON 0x39 WM_COMPAREITEM 0x41 WM_COMPACTING 0x44 WM_COMMNOTIFY (obsolete in Win32) 0x46 WM_WINDOWPOSCHANGING 0x47 WM_WINDOWPOSCHANGED 0x48 WM_POWER 0x4A WM_COPYDATA 0x4B WM_CANCELJOURNAL 0x4E WM_NOTIFY 0x50 WM_INPUTLANGCHANGEREQUEST 0x51 WM_INPUTLANGCHANGE 0x52 WM_TCARD 0x53 WM_HELP 0x54 WM_USERCHANGED 0x55 WM_NOTIFYFORMAT 0x7B WM_CONTEXTMENU 0x7C WM_STYLECHANGING 0x7D WM_STYLECHANGED 0x7E WM_DISPLAYCHANGE 0x7F WM_GETICON 0x80 WM_SETICON 0x81 WM_NCCREATE 0x82 WM_NCDESTROY 0x83 WM_NCCALCSIZE 0x84 WM_NCHITTEST 0x85 WM_NCPAINT 0x86 WM_NCACTIVATE 0x87 WM_GETDLGCODE 0xA0 WM_NCMOUSEMOVE 0xA1 WM_NCLBUTTONDOWN 0xA2 WM_NCLBUTTONUP 0xA3 WM_NCLBUTTONDBLCLK 0xA4 WM_NCRBUTTONDOWN 0xA5 WM_NCRBUTTONUP 0xA6 WM_NCRBUTTONDBLCLK 0xA7 WM_NCMBUTTONDOWN 0xA8 WM_NCMBUTTONUP 0xA9 WM_NCMBUTTONDBLCLK 0x100 WM_KEYFIRST 0x100 WM_KEYDOWN 0x101 WM_KEYUP 0x102 WM_CHAR 0x103 WM_DEADCHAR 0x104 WM_SYSKEYDOWN 0x105 WM_SYSKEYUP 0x106 WM_SYSCHAR 0x107 WM_SYSDEADCHAR 0x108 WM_KEYLAST 0x10D WM_IME_STARTCOMPOSITION 0x10E WM_IME_ENDCOMPOSITION 0x10F WM_IME_COMPOSITION 0x10F WM_IME_KEYLAST 0x110 WM_INITDIALOG 0x111 WM_COMMAND 0x112 WM_SYSCOMMAND 0x113 WM_TIMER 0x114 WM_HSCROLL 0x115 WM_VSCROLL 0x116 WM_INITMENU 0x117 WM_INITMENUPOPUP 0x11F WM_MENUSELECT 0x120 WM_MENUCHAR 0x121 WM_ENTERIDLE 0x132 WM_CTLCOLORMSGBOX 0x133 WM_CTLCOLOREDIT 0x134 WM_CTLCOLORLISTBOX 0x135 WM_CTLCOLORBTN 0x136 WM_CTLCOLORDLG 0x137 WM_CTLCOLORSCROLLBAR 0x138 WM_CTLCOLORSTATIC 0x200 WM_MOUSEFIRST 0x200 WM_MOUSEMOVE 0x201 WM_LBUTTONDOWN 0x202 WM_LBUTTONUP 0x203 WM_LBUTTONDBLCLK 0x204 WM_RBUTTONDOWN 0x205 WM_RBUTTONUP 0x206 WM_RBUTTONDBLCLK 0x207 WM_MBUTTONDOWN 0x208 WM_MBUTTONUP 0x209 WM_MBUTTONDBLCLK 0x20A WM_MOUSELAST 0x20A WM_MOUSEWHEEL 0x210 WM_PARENTNOTIFY 0x211 WM_ENTERMENULOOP 0x212 WM_EXITMENULOOP 0x213 WM_NEXTMENU 0x214 WM_SIZING 0x215 WM_CAPTURECHANGED 0x216 WM_MOVING 0x218 WM_POWERBROADCAST 0x219 WM_DEVICECHANGE 0x220 WM_MDICREATE 0x221 WM_MDIDESTROY 0x222 WM_MDIACTIVATE 0x223 WM_MDIRESTORE 0x224 WM_MDINEXT 0x225 WM_MDIMAXIMIZE 0x226 WM_MDITILE 0x227 WM_MDICASCADE 0x228 WM_MDIICONARRANGE 0x229 WM_MDIGETACTIVE 0x230 WM_MDISETMENU 0x231 WM_ENTERSIZEMOVE 0x232 WM_EXITSIZEMOVE 0x233 WM_DROPFILES 0x234 WM_MDIREFRESHMENU 0x281 WM_IME_SETCONTEXT 0x282 WM_IME_NOTIFY 0x283 WM_IME_CONTROL 0x284 WM_IME_COMPOSITIONFULL 0x285 WM_IME_SELECT 0x286 WM_IME_CHAR 0x290 WM_IME_KEYDOWN 0x291 WM_IME_KEYUP 0x2A1 WM_MOUSEHOVER 0x2A3 WM_MOUSELEAVE 0x300 WM_CUT 0x301 WM_COPY 0x302 WM_PASTE 0x303 WM_CLEAR 0x304 WM_UNDO 0x305 WM_RENDERFORMAT 0x306 WM_RENDERALLFORMATS 0x307 WM_DESTROYCLIPBOARD 0x308 WM_DRAWCLIPBOARD 0x309 WM_PAINTCLIPBOARD 0x30A WM_VSCROLLCLIPBOARD 0x30B WM_SIZECLIPBOARD 0x30C WM_ASKCBFORMATNAME 0x30D WM_CHANGECBCHAIN 0x30E WM_HSCROLLCLIPBOARD 0x30F WM_QUERYNEWPALETTE 0x310 WM_PALETTEISCHANGING 0x311 WM_PALETTECHANGED 0x312 WM_HOTKEY 0x317 WM_PRINT 0x318 WM_PRINTCLIENT 0x358 WM_HANDHELDFIRST 0x35F WM_HANDHELDLAST 0x380 WM_PENWINFIRST 0x38F WM_PENWINLAST 0x390 WM_COALESCE_FIRST 0x39F WM_COALESCE_LAST 0x3E0 WM_DDE_FIRST 0x3E0 WM_DDE_INITIATE 0x3E1 WM_DDE_TERMINATE 0x3E2 WM_DDE_ADVISE 0x3E3 WM_DDE_UNADVISE 0x3E4 WM_DDE_ACK 0x3E5 WM_DDE_DATA 0x3E6 WM_DDE_REQUEST 0x3E7 WM_DDE_POKE 0x3E8 WM_DDE_EXECUTE 0x3E8 WM_DDE_LAST 0x400 WM_USER 0x8000 WM_APP