Decent mic, good preamp?

Have you tinkered with using the vocal categories for plugins? May learn a lot just playing around with the settings. (Right-click and select track category-vocal category then allow plugins to be inserted) Just something to try that is built into the programs already (RB and PT).
Do this on a copy of the existing song, of course, so you don't mess up what you already have.

Otherwise-
Four slots available on the track DX FX area, typical things to try here;
EQ the voice track, remove everything in the very bottom end to clean up. See what else helps with the character.
Put a de-esser on the track if needed SpitFish is a decent free one. Removes some sibilance and makes you not so 'right in your ear' sounding.
Put a compressor on the track, many professionally recorded vocals go thru a compressor.
Kjaerhaus Classic Compressor vocal presets are nice (and free). BlockFish (same company as spitfish) is another nice free one.
http://www.digitalfishphones.com/main.php?item=2&subItem=5

A little reverb, adjust to suit, depending on song. I like 'Ambience' because of the quality and ability to EQ the reverb right inside the module, and adjust damping on top and bottom. Nice plugin with a free version (nag screen) and not too expensive to license. They have worked with PGMusic in the past to make the plugin behave better in PT, so I have supported them since. There are TON of presets in this plugin, so it may take a while to find what you like, unless you know your way around a reverb unit.

**Note- just noticed Ambience free no longer has nag screen
http://magnus.smartelectronix.com/#Ambience

I do not work here, but the benefits are still awesome
Make your sound your own!