Just to supplement Cannonade's answer, here's the html/css that a Google Map control uses. You can replicate the css to make it look just like the real thing.
You could create a formal GControl, or you could just place them over the Google Map with absolute positioning.
Active button:
<div style="border: 1px solid black; position: absolute; background-color: white; text-align: center; width: 5em; cursor: pointer; right: 15.3em;" title="Show street map">
<div style="border-style: solid; border-color: rgb(52, 86, 132) rgb(108, 157, 223) rgb(108, 157, 223) rgb(52, 86, 132); border-width: 1px; font-size: 12px; font-weight: bold;">
Map
</div>
</div>
Inactive button:
<div style="border: 1px solid black; position: absolute; background-color: white; text-align: center; width: 5em; cursor: pointer; right: 5.1em;" title="Show imagery with street names">
<div style="border-style: solid; border-color: white rgb(176, 176, 176) rgb(176, 176, 176) white; border-width: 1px; font-size: 12px;">
Hybrid
</div>
</div>
UPDATE: There is also an extension in the Google Maps Utility Library that can accomplish this -
ExtMapTypeControl