I'm not quite sure which bands you have already tried, and which you liked, but here are some of my top picks, and a bit how they sound, seeing as post-rock is a fairly wide genre.
(Alphabetically):
65daysofstatic - Nice mix of Electronic-influences with the Post-Rock sound. Seeing as you like Maybeshewill, these guys aren't THAT different, they do have an Electronic-influence that Maybeshewill doesn't, but they're also fairly Math-Rock influenced as well.
Codes in the Clouds - These guys are fairly indie, haven't quite gotten big yet, but they have only released 2 ½ albums, the ½ is a remix-album. They're more towards the melodic and catchy-side of Post-Rock, I would say that they are bit like Explosions in the Sky, except not as "repetitive", to me at least.
God Is An Astronaut - A band with more variety then your average Post-Rock band. As for what makes their sound unique, I would probably say that they use keyboards more, or in a way that makes me think of them as a bit more keyboard-oriented at least. It's a nice feature to create soundscapes though, really digging it.
Godspeed You! Black Emperor - Highly regarded not only within the genre, but also on this forum. Very orchestral, long and epic songs, and I think that albums like "Lift Your Skinny Fists Like Antennas..." and "F♯ A♯ ∞" are classics that all Post-Rock fans should have checked out.
Mogwai - One of my favorites, and one of the bigger bands in the genre. In terms of variety, I don't think there are too many bands that can beat Mogwai, because they utilize pretty much all the instruments they use, in a good way.
Some songs are more piano/keyboard-driven, some are just heavy 'in-your-face' with powerful guitars, and some of them have cool epic soundscapes. In other words, I think most Post-Rock fans can find stuff by Mogwai that they will enjoy.
Mono - Recently discovered, but these guys are really good. Hard to put my finger on exactly what I like, but they are masters at build-up songs, and they can create atmosphere like very few others can.
Sigur Rós - A few would most likely argue about if Sigur Rós are actually "pure" post-rock or not, but I think that comes mostly from the fact that Sigur Rós has vocals, which isn't really that common within the scene.
There are other great bands within post-rock that has vocals, Gregor Samsa comes to mind, but as I said it's a bit unusual, but everything with Sigur Rós is fantastic really.
They sorta have a "down to earth"-feel, which is very clear if you watch their DVD, "Heima" where they are outside in the nature, playing some of their songs, just chilled back.
They also cover a lot of ground, and one of my favorite bands.
These are some of my top picks, I would take my time to describe more bands, but that would take some time.
Anyhow, I'll list a few more ones that I really like, and if they seem interesting, I can always try to describe them as well:
A Silver Mt. Zion
And So I Watch You From Afar
Ef
Explosions in the Sky
From Monument to Masses
Gregor Samsa
Her Name is Calla
If These Trees Could Talk
iLikeTrains
Jakob
Long Distance Calling
Maybeshewill
Red Sparowes
Russian Circles
The American Dollar
This Will Destroy You
Tortoise
Vessels