This is a list of the JOSM plugins that I either have installed now or that I had problems with in the past along with comments on each.
ElevationProfile Can be helpful when determining if a street is on an incline or decline.
FixAddresses Not very helpful because if a building has more than one node each node is listed as having its own address. So the list it create are often to long to be useful.
geotools - Was installed by another plugin
GPSBlam I haven't spent enough time with it to know how to properly use but it sounds like I should.
GPXFilter I'm not sure if this is needed or if it is installed by default.
ImageWayPoint - I might be using it or I might be using another plugin that does basically the same thing I'm really not sure.
InfoMode Can be helpful when dealing with multiple GPS traces a the same time.
jts - Was installed by another plugin
Kendzi3D-jogl - Was installed by Kendzi3D which often caused JOSM to crash so I uninstalled Kendzi3D but it must have left Kendzi3D-jogl behind.
log4j - Was installed by another plugin
MapDust Sounded like it would be really helpful when I installed it but I haven't been using it.
measurement - I haven't found this to be very useful
namemanager - It sounds like it might be helpful but I don't think I've been using it
OpenData I think I was trying to use this to added some missing towns that are around Syracuse but after reading the WARNING on the WIKI I decided not to use it.
OpeningHoursEditor Makes it easy to set hours for businesses but it should obviously only be used with businesses that have constant hours.
OpenStreetBugs I haven't really been using it but I don't know why.
openvisible - I don't think it works
Photo_Geotagging Very helpful for making GEO tagged on photos more accurate by default on my Android phone the photos are really off so I would correct them before they were uploaded to OpenStreetView.
print - Helpful if you need to print parts of the map
restart - Helpful when you install as many plugins as I have
Reverter Sounds like a good idea but I don't think I've used it since I've installed it.
RoadSigns I was trying to add some deer crossing signs which I didn't end up doing. However, I think I've been using it for some other signs without even knowing or at least remembering it was a plugin.
Tag2Link Helpfully when adding wikipedia page because there supposed to look like this "wikipedia=en: U.S. Route 11 in New York" and not just a url
turn_lanes#Plugin Could be helpful in the future but should not be used now because it uses a relation that has not been implemented into the API and if your not sure if you should use a relation
TurnRestrictions Anything that makes dealing with relations easer and safer is great plus turn restrictions are also one of the few relations worth messing with.
Undelete Sounds like a good idea but I don't think I've been using it.
UtilsPlugin2 Should be installed by default
VideoMapping Sounds like a great idea but it always crashes JOSM for me.
WayDownloaderPlugin Should be installed by default! It's great for long tracks because it allows me to download all the mapping data I need in one go and it prevents me from having to download areas that are visible on the screen but that I wasn't really anywhere near.
waypoint_search - Makes finding all of the tags I recored much easer especially when I'm using the Bing satellite images
Wikipedia It should help you find wikipedia pages but it doesn't seem to work for me most of the time
Ok the really crazy thing is that I haven't installed all of the plugins so if you used a plugin that you think is great post a comment about it or if you have a similar list post a link to it.