If you don't like the flashlight idea because you need both hands to work on something and you don't feel like wiring a new light, here few more options:
>These lights are 12V fluorescent, portable and they plug into your lighter and some have aligator clip that can be hooked up to your battery terminals. On the 300 the battery is in the trunk but you have boosting option under the hood too. Like the flashlight you can use it anywhere around the car if you the one with the long wire.
>There is also LED lights used mainly for outdoor lighting but can be use for under too since it's 12 volt.
>For people who has cordless power tools, there is also a fluorescent light option that you can get that mount onto your battery pack.
>Here few links that I selected and my favorite one is the last one. $12.00, hooks anywhere, plugs into the lighter and has aligator clips.
· http://www.nextag.com/Bayco-12-Volt-Cool-524763089/prices-html?nxtg=2a5700a1c0506-28D1632A1A356B07
· http://www.lindequipment.net/stubby.htm
· http://12volt.com.au/redirect.html?a=/General%20Htmls/webcat2003/lights.html
· http://www.sunvoltssolar.com/SVinoutlights.htm
· http://www.builderssquare.com/xp_62063-14_4V_12V_Fluorescent_Area_Light_DC528_DeWALT.aspx
· http://www.matcotools.com/Catalog/toolcatalog.jsp?cattype=T&cat=2357
· 
http://www.amazon.com/Trademark-Global-Fluorescent-Work-Light/dp/B000OUZN6M