This is Eric Meyer's CSS reset, which you can use, for example, to override CSS that you might not have access to.

Minified Version

html,body,div,span,applet,object,iframe,a,abbr,acronym,address,big,cite,code,del,dfn,em,font,img,ins,kbd,q,s,samp,small,strike,strong,sub,sup,tt,var,dl,dt,dd,ol,ul,li,h1,h2,h3,h4,h5,h6,pre,form,fieldset,input,textarea,label,legend,p,blockquote,table,caption,tbody,tfoot,thead,tr,th,td{margin:0;padding:0;border:0;outline:0;font-weight:inherit;font-style:inherit;font-size:100%;font-family:inherit;vertical-align:baseline;}body{line-height:1;color:black;background:white;}:focus{outline:0;}table{border-collapse:collapse;border-spacing:0;}caption,th,td{text-align:left;font-weight:normal;}fieldset,img{border:0;}address,caption,cite,code,dfn,em,strong,th,var{font-style:normal;font-weight:normal;}ol,ul{list-style:none;}h1,h2,h3,h4,h5,h6{font-size:100%;font-weight:normal;}blockquote:before,blockquote:after,q:before,q:after{content:"";}blockquote,q{quotes:"" "";}abbr,acronym{border:0;}

Legible and Expanded Version

html, body, div, span, applet, object, iframe,
h1, h2, h3, h4, h5, h6, p, blockquote, pre,
a, abbr, acronym, address, big, cite, code,
del, dfn, em, font, img, ins, kbd, q, s, samp,
small, strike, strong, sub, sup, tt, var,
dl, dt, dd, ol, ul, li,
fieldset, form, label, legend,
table, caption, tbody, tfoot, thead, tr, th, td {
    margin: 0;
    padding: 0;
    border: 0;
    outline: 0;
    font-weight: inherit;
    font-style: inherit;
    font-size: 100%;
    font-family: inherit;
    vertical-align: baseline;
}
/* remember to define focus styles! */
:focus {
    outline: 0;
}
body {
    line-height: 1;
    color: black;
    background: white;
}
ol, ul {
    list-style: none;
}
/* tables still need 'cellspacing="0"' in the markup */
table {
    border-collapse: separate;
    border-spacing: 0;
}
caption, th, td {
    text-align: left;
    font-weight: normal;
}
blockquote:before, blockquote:after,
q:before, q:after {
    content: "";
}
blockquote, q {
    quotes: "" "";
}

Source: http://meyerweb.com/eric/thoughts/2007/05/01/reset-reloaded/

Yahoo has a great CSS reset they make available which they heavily test against major browsers and multiple versions. http://developer.yahoo.com/yui/reset/