everyone forgot about the Toneblaster X that sub mentioned!
It's clean channel is pretty dynamic and clear, breaks up when you turn the gain high. the X channel is really all you need, it has a mid-sweepable function that goes everywhere in the distortion world, more than enough for an amp the size and price. one of the members in my club has one, we played it in the school hall and it was definitely projectiing and articulate for a mere 15 watts in an open area.
Also, don't forget to give yourself more gain than pop-rock gain, you'd need it. Many beginners end up having to get something different when they move on from the kind of music they started out with, myself being that.
get an amp that won't limit your creativity, the roland cube is great, the toneblaster X is even more versatile and "plug-and-play" imo. But if you need the built in effects of the Cube30, go for it.
And also, tubes don't like to migrate that much, get a reliable solid-state piece.
(p.s you might want to get a Peavey Blazer, great amp for rock gain uses and very reliable, though others would say otherwise...THE CHOICE IS YOURS!)