The nicest transmitters i've found are Linx TXM-433. They are not cheap -- $12 or so -- but are good quality with nice features.
The cheap ones are hard to pass up at $2 or less even, but I have found them highly variable in power output, output impedance, and most frustrating for me, start-up time. Startup time varies from 10us to as much as 80us unit to unit and this affects signal timing. I have fallen into the habit of individually characterizing the startup time and putting this in a calibration constant for the signalling protocol. It's a major PITA, but seems to be sufficient for my needs.
If you find a source for cheap consistent modules, please post here.
I don't know what you use for receivers, but the Linx receiver is a nice one too. One feature it has is an RSSI indicator output that is really useful in debugging and unit placement. Most of the cheap receivers are actually quite good superhet designs, but lack RSSI output. I found some based on a Princeton PT4301-X superhet receiver chip that I've managed to tack a line onto one of the signals to get an RSSI output, but that's a major hassle and I've destroyed more than one attempting the job.