You could also try propping up a couple of mattresses and record in between them (especially if you're working with a strictly drywalled room)
Have you tried using the SiR (I think that's what It's called) Impulse Response reverb (free vst) - I think cubase comes with o.k. stock plugins though - never tried the reverb
I find that Vocals are a real trick - Here's what I've found to be the best place to start with fixing up vocals to sound decent, even when recorded in crappy rooms - Note that there is no quick way, if any way, to compleley fix a poor source recording. So as off-topic as this might appear - I think it might help. You can use this little trick pretty well universally to 1) find and fix problems and 2) to find solutions to areas in a track that are lacking.
Use an EQ, Set the Q fairly low, but not too low - enough so that it affects maybe 1 entire octave, and sweep accross the entire frequency spectrum at a moderate gain (+6dB) and moderate speed .. you will hear the different tones of each octave sticking out, but you will notice that certain spots stick out FAR more than the rest and make things sound horrid. Those are your problem areas - watch out for circa 250hz - those are your vocal fundamentals (by 250 I mean anything in that octave)
Take the Q up to something middle-of-the-road and narrow in on each of the problem areas one by one - be meticulously careful here - everything will start to stick out, but close listening will reveal that certain areas in the narrow bands stick out further ... once you know where the probelms are, you can start dipping - for problems in the higher half of the spectrum, use a de-esser to clamp the S and Shhh sounds a little)
Once you have the EQ out of the way, pick a reverb and mix to taste - you can try dampening the lows on the re-verb to get it a little brighter sounding without actually boosting the highs - just make sure you have enough of the original singal in there that your vocal track can still be up front in your mix.
Now I don't know what monitoring you are using, but good monitors will make a HUGE difference in your perceptions.