You can use SyntaxHighlighter, the author has provided a hosted version so you just have to go to your blog template, choose edit HTML and add following code to the beginning of the page
<link href='http://alexgorbatchev.com/pub/sh/2.0.320/styles/shCore.css' rel='stylesheet' type='text/css'/>
<link href='http://alexgorbatchev.com/pub/sh/2.0.320/styles/shThemeDefault.css' rel='stylesheet' type='text/css'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shCore.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushJScript.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushPowerShell.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushDiff.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushCpp.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushCSharp.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushBash.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushPlain.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushXml.js' type='text/javascript'/>
<script src='http://alexgorbatchev.com/pub/sh/2.0.320/scripts/shBrushSql.js' type='text/javascript'/>
<script type='text/javascript'>
SyntaxHighlighter.all();
</script>
You can see example on my blog