I've been using a bench grinder for years which works OK for me, but it ain't pretty.
Then recently I came across this thread about using a 60 grit zirconia flap wheel on a 4.5" angle grinder. Pretty much what bakerg is talking about. There's a photo in that thread which shows a guy's first time results using this method and it looks better than what I've been doing. I blew a double sawbuck on a Harbor Freight angle grinder many moons ago to use with cut-off wheels, so I'm all over it. I also use one of those plastic cone-looking blade balancers to keep things legit.
This will be the first season I actually look forward to blade sharpenings because I just got a Mojack EZ from Tractor Supply Hardware, along with two fancy rubber wheel chocks for the rear wheels. I've been playing around with that Mojack and it's something else. For years I've been jerking around with my floor jack, jackstands, and/or ramps which leave little room to work, but with the Mojack I can easily crank my ZTR up until the rear hitch very nearly touches the garage floor. I'm not big on single use tools, but I'm glad I broke my principles this time because there's enough room under that deck now to play handball, and the mower seems very safe and secure. I believe my grass is going to look EXTRA tasty this spring and summer.