I have an old HP laserjet 5p that does a great job on envelopes. A rear door opens to create a straight paper path. This printer also handles failrly heavy card stock well.
All of the top feed Canon inkjets I've owned have printed stacks of up to 20 #10 envelopes without any problems. My latest envelope task (using my iP4000) was addressing over 200 wedding invitation envelopes. Every envelope came out perfect - not a single reject.