B&W Nautilus 805s...and here's why:
This response takes this topic in a slightly different direction. Most of the responses are in the vein of "I really, really like speaker X and can't see myself upgrading." I see this topic really asking the question "What speaker would you never get rid of?" There is a difference.
Is the Nautilus 805 the *best* sounding speaker out there? Of course not. However, I will *never* get rid of my (4) Nautilus 805s because I will *always* have a use for them.
What audio enthusiast doesn't have a use for a great sounding, great looking monitor / bookshelf sized speaker? Even if they are not part of my primary system, they would be great in a den, a living room, bedroom, or even an office. They will work in a one-bedroom apartment as well as they would integrate into a room of a 12,000 sq ft mansion.
It's tough to deny the beauty and craftsmanship of the Nautilus 805s (especially in natural cherry). If you can help the wife get past the "microphone" on the top, you can probably integrate these speakers into the decor of most any room.
Some may not care for the signature B&W sound, but these speakers are undeniablly respectable. The measure well (as long as you are not a dog) and are nearly time aligned. They aren't too picky about placement, but given sufficient breathing room, can "disappear" into the music.
They are easy to drive, and work with high-powered solid state amps as well as tube setups (probably not SET, but I've never tried it). The 805s rolloff nicely such that integration with a sub (especially a REL Strata III) is a breeze.
My next speaker will probably be the Vandersteen 3A sigs + (2) 2Wq subs. However, I won't feel the same loyalty to that setup as I do for my 805 / Strata III combo. Why? One word - flexibility.
I look forward to my next upgrade, but I will not be selling my 805s to do so. For they are speakers I will hold onto for life.