Caramunich will make a beer pretty orange, if it's with only base malt. I used this for the first time in a saison recently, it came out with a really vibrant, sunny orange color.
If you want it really orange, I'd do something turbid like a Witbier, then add a boatload of orange food coloring. The turbidity of the witbier will help make the orange brighter.
Also, I'd practice on a commercial bottle before committing to a whole batch using this method!
Wasnt there a "Sweet Potato ESB" recipe in a recent BYO that resulted in a bright orange beer (but with no taste of sweet potato)? I have considered brewing it for Halloween!