+1 to the FullDrive 2. It's got a great bluesy tone all by itself on the clean channel. Tends to get a bit dark on the dirty channels, so adjust your EQ accordingly. The GT-500 also has a great OD. It's got a built-in separate distortion effect as well, but I'm not a huge fan of the distortion's overall tone, and the outrageously adjustable mid boost/cut control is a bit gimmicky since you'll never need that much boost nor that much cut, plus the frequencies it controls aren't my preference anyway.
Actually, the OCD makes a great stand-alone crunch tone for the clean channel. Anything from edgy clean Beatles-type tone to crunchy Zep, AC/DC, James Gang kind of classic crunch.
I know you don't quite have the same option with a Roadster, but one of my favorite tricks is to set my Triple Rec's clean channel to Pushed, treble and mids dimed, bass at 2:00, and run my modded Bad Monkey in front of it. I can get the nicest open-toned Marshall crunch out of that combo that gets me anything from the lightest Zep to classic metal riffs like Maiden, Dio, Priest, etc. I modded the Bad Monkey to give me a stronger mid response with more even-order harmonics for leads.