I recommend the Chinese-manufactured CZE-7C. I have a couple of these and have been running them for a couple of years now. They are switchable between 1 and 7 watts and run off a standard 12VDC 3a power supply. I was suspicious of harmonics and birdies so I studied one using a spectrum analyzer after I fired it up for the first time. There is little, if any sign of any nasty harmonics. It is a true FM stereo unit. It's switchable to any frequency in the Japanese and US bands. (On one of my units it fired up once and was not restricted to the FM bands but allowed tuning way up to 150 MHz or so, but the other one doesn't exhibit that anomaly). Drawbacks: there is a built-in limiter that squashes most compression/limiting you can do before feeding the audio, so I've found it's best to feed it a nice clean input that's not over-processed.
I recently acquired a CZE-15A, which is the bigger brother of the CZE-7C. The 15A is switchable between 5 and 15 watts. I haven't had a chance to test this one out thoroughly as yet.
These units can be had for less than $100 via many resellers on Amazon. As always be careful of the overseas resellers and look for positive feedback.
Overall these units are very nice and have a great price/performance mix.