purelytoptv.com is a good place where you can watch all of the Glee episodes online. although you can only watch 72 minutes before having to wait an hour, its the only place I've found so far and I watch a lot of Glee episodes on that website.
tv shack
There are many websites you can watch Glee for free. My personal fav is Megavideo. You just have to type in the name of the show and it bring it up for you. You can also use it for different shows. :)
Hulu offers the most recent 5.
go on bbc iplayer and type in glee and it will come up with all the series of glee
You can watch all seasons on FevsTV.com
go on fox.com click on watch episodes, then scroll down the page until you see glee, click on it, and it has the 5 recent episodes, but in between them are commercials you cant skip, but they only last under 2 minutes
You can watch it on youtube but I don't know if that website has all of them but I did see all of the beast episodes but not beast plus episodes
seesaw
Try Hulu, tvduck, or fancast also on fastpass tv which has great quality of the episodes you can go onto fox.com. the quality is great and its on 1 day after the episode was aired. The only bad thing is that there are still ads, but not too many. if u want to watch it for free go to blinkx remote
I go to hulu and watch-series.com. If you go to watch-series, I totally recommend using the mega-video links, they buffer quickly. But, you can only watch 72 minutes, and then you have to wait awhile before you can watch more.
No you cannot watch all episodes online but if you go on to youtube and type in "mihighepisodes" (all one word), then it comes up with some episodes of Series 1 & 2 (Recommended)