Good Monitors for no more than 150?

Maybe a used pair of Paradigm Atoms? Any version will do. For new speakers in that price range, some Polk monitors give decent bang for the buck, IMHO.

cambridge audio 6.

This is an easy one, the Roth Audio OLi1, a solid and beautiful British minimonitor with great sound for $150. Read my reviews at Amazon and Audio Circle.

I forgot to add a rave review of the OLi1 by What Hi-Fi? magazine.

If you're willing to go up to $200/pr, you could snag one of the last closeout pairs of Athena LS-300 towers (retail $500/pair) from Audio Advisor. I always liked the speakers from API: Good tonal balance, smooth, neutral, works well with all kinds of music. These floorstanders will also give you more of the bottom octave than most sub-$200 contenders.

At your target $150/pair, you'd be hard-pressed to beat the Energy C-200. 88dB sensitivity, bass into the low 40's/high 30's, handles up to 125 watts, excellent room-filling dispersion, good transparency and detail in a natural perspective, especially at that price.