All of these bands are, imo, quite good but have currently less than 25.000 listeners.

Johnnytwentythree
Amazing band. Is a must if you like emotional postrock with strings.
My favorite tracks: Into the Depths, Holy Ghost People, Red Bird, Fall of Swords, Procession, N.T.

Beware of Safety
The way they build up the intensity is amazing. Highly recommended.
My favorite tracks: To the Roof! Let's Jump and Fall, Kaura, The Difference Between Wind And Rain, Circa, Weak Wrists, Raingarden

Mooncake
For those who like cello in postrock. Novorossiysk 1968 is something special.
My favorite tracks: Novorossiysk 1968, Message From Arecibo, Rain in the Ashtray, Nine Billion Names... (to A.Clarke)

Giants
My favorite tracks: O' Tide, Vessels, While The Ages Steal

Ours to Alibi
My favorite tracks: Eight, Weary, We Fell Upon Land, Nine, ... and Then We All Made Kites, Four

For a Minor Reflection
Postrock from Iceland. These guys have recently toured with Sigur Ros.
My favorite tracks: Fallegt útsýni, Óhljóð, Reistu þig við, sólin er komin á loft...

I Hear Sirens
My favorite tracks: Like A Leaf From A Tree In Its Dying Season, This Is The Last Time I'll Say Goodbye

Followed by Ghosts
My favorite tracks: City of Noise, Clear Blue Sky, A Mirthful Experience, The Entire City Was Silent

Cecilia::Eyes
These guys are pretty good. Bass is incredible in most of the songs.
My favorite tracks: Song For Alda, Too Late For A Porn Movie, One million whales, Our Longest Winter

Sleepmakeswaves
My favorite tracks: It's Dark, It's Cold, It's Winter, What We Cannot Speak of Must Be Passed Over In Silence

Wood and Wires
Amazing blend of guitars and violin.
My favorite tracks: Gienah Cygni, Vega, Archernar

Final Days Society
My favorite tracks: (The) Fire, Violent Red, Silence is…, Scalar Fields

Long Distance Calling
Postrock from Germany based on heavy guitar riffing. Highly recommended for listeners of Russian Circles and If These Trees Could Talk.
My favorite tracks: I Know You, Stanley Milgram!, Sundown Highway, Jungfernflug

Change of Plans
They are from Istanbul / Turkey. Close your eyes and enjoy beautiful music.
My favorite tracks: Conversationalist, Bugun Bitsin, Igloo

We're From Japan!
My favorite tracks: Run Shoot Don't Panic, Black Bag Work, In Every Hive, A Queen

The Ascent of Everest
My favorite tracks: Alas! Alas! The Breath of Life!, Molotov

Dorena
Postrock from Sweden.
My favorite tracks: Till Våning Tretton, En Tonårsromans, Dagsländan

The Severely Departed
My favorite tracks: No Help Comes, Closer to Home, Exhale

Moonlit Sailor
My favorite tracks: Waterwall, Once We Were Children, Yes

Exxasens
Postrock with progressive metal and electronic influences. Highly recommended for listeners of God is an Astronaut and Maybeshewill.
My favorite tracks: Your Dreams are My Dreams, Polaris

3epkano
Decent postrock with cello and viola.
My favorite tracks: Snowball, Hotrs, Everybody Is Already Down Below

Youth Pictures of Florence Henderson
My favorite tracks: We May Be Remembered by What We Did When We Sat Down, A List Not to Be Read at Your Wedding, How Odd to See These Lamps Still Burning

Tunturia
My favorite tracks: Cast Shadows on Clouds, Satellites

miaou
My favorite tracks: Future Pavilion, A Bird in the Hand

Sunlight Ascending
A young band from US. Pretty good.
My favorite tracks: Out of This Place, Out of This Place II

Codes In The Clouds
My favorite tracks: Fractures, Don't Go Awash in This Digital Landscape

Nyctalgia
My favorite tracks: Time Changed Everything, Falling Into Nothingness

New Century Classics
These guys have so much potential. Amazing experimental music with violins.
My favorite tracks: Congratulate You, Where?, Drift Motion, Room Two, Postcards

1099
A new band to follow. Up! Up! Up! is something special.
My favorite tracks: Up! Up! Up!, Beauty of the Night

Shapes Stars Make
They are from Texas. They work with John Congleton. Two solid reasons to check out a band.
My favorite tracks: Be Gentle, Young One, The Hurting, Giant Bird, This is Epic

Glass America