First of all every "shop" needs a clock. There are some great reproduction clocks with automotive logos and themes, and you can find a variety of these clocks at swap meets and antique stores.
http://www.automobiliausa.com/furniture.html
or this stuff...
http://garage-toys.com/gafu.html
There are other great accessories too after all, when your buddies come by, they'll need places to sit. To really offer a retro and hot rod look, check out these couches from Corbin.
http://www.corbin.com/furniture/
You could use Grant or Lecarra steering wheels for wall art or end tables etc. You can add other accessories to your garage like are die-cast models of your favorite cars and let's not forget about the walls of your garage.
http://www.diecastmodelcars.com/
http://www.diecastmuscle.com/index.jsp
http://www.ediecast.com/
Hemming's Motor News offers a variety of great calendars with different themes from Muscle Cars to Abandoned Trucks! Also, look for old movie posters with car or racing themes, as well as vintage or reproduction metal car signs and wallpaper.
http://www.hemmings.com/
These and other items can also be found at flea markets, antique stores, or at online auction sites. Some of the great things about these items are that they allow you to personalize your "garage", and make it more entertaining for yourself and for those folks who drop by.
Another luxury would be a vintage jukebox, which is always cool.
These sites are also very cool and have images of some garage projects that you could look to for inspiration.
http://www.thegarageproject.com/products/index.htm
http://www.mygaragestore.com/
Retro-fabrics are also available. Check Ebay and others. It doesn't cost that much to make slip covers or you could re-upholster in a fabric of your choice...or have one designed with flames etc...
You could also replace one or more of your cabinets with "Craftsman" or other tool chests/cabinets.
So it's up to you how far you want to go, but keep it in mind that the point is to have fun!