Another TASCAM 16x08 here.  Great interface for me.  Doesn't have 16 line inputs though.  Even the 20x20 is split up ... or rather it will be when released.
 
 

Allen & Heath ZEDR16 and love it.

Focusrite 18i20. Rock solid performance, great sound and fantastic customer service.

Focusrite Pro40.  Been a solid piece of my arsenal. 
Performs well and sounds good.  Drivers have been solid and updates work without a hitch. 
There are other interfaces I drool over, but this one has been consistent (what more can you ask for?)

After many years using an M-Audio Firewire 1814 I recently purchased an Antelope Orion 32 (with the MP32 Mic- Pre's). I cannot say that I have mastered this thing yet, but so far it's been awesome.  Admittedly it's pretty pricey but I am loving the 32 channels of I/O!  No need to worry about linking units to expand I/O with this interface!

I use 2 roland octacaptures one slaved to the other offering me 16 inputs xlr or 1/4 trs balanced, used it to record our 3rd cd on sonar x2 or x3 with no problems.

Love my roland octacapture , and as mentioned you can chain two together ( not done that yet ) , you can pick up these nowadays for a lot less than I paid . 
Ric
 

Thanks for all the replies, so far! I find it very interesting to see what other folks are using and what works well for them.
Seems like a lot of Focusrite users.
I am kind of surprised there are not a lot of Presonus users. Makes me wonder if there may be issues with Presonus and Sonar or, if they are just not that popular?
 

Using  a Focusrite Scarlett 18i8, with the extra 8 inputs via ADAT from a Behringer ADA8200.
Lexicon MX300 connected to the Scarlett via S/PDIF.
 
Had to spend a bit of time with the Scarlett MixControl software to wrap my head around all the routing possibilities - 
but everything works great!!

Can't really go wrong with RME or Antelope. The Antelope stuff sounds great (kinda jealous of the previous posters MP32....I use a bunch of discrete pre's...they're nice but can be clunky to use) and the RME stuff is fantastic is well. You'll pay more for them, but it's totally worth it IMHO. Only drawback with the Orion is the limited routing. It only has one "mix" stereo pair output so you can't do multiple headphone mixes or have multiple sources feed a single output pair. 
 
Oh, I use an RME HDSPe MADI fx feeding an Orion 32 and an Lynx Aurora 16.
 
Dean