I know of no standard, but perhaps it's most common to use naturals and sharps: C, C#, D, D#, etc. I don't see any problem in this context in terms of implying any sense of key.
Organ pipes and many electronic tuners label notes using naturals and sharps, although the German note labeling convention uses the name "B" for what might otherwise be called "A#", and "H" for what might otherwise be called "B".
@Tim - depends on the flat. Bb is okay, but Fb is definitely depressing.
Actually, for me, the problem doesn't arise much any more: since I nowadays play almost exclusively heptatonic music, either tuned justly (usual scale: 8 9 10 11 12 14 15) or in some sort of meantone (C D E F G A B, the tuning being either more thirdy or more fifthy depending), then I'm never faced with the problem of denoting tones in a value (key) free way.
@ScottWallace - Virtually all jazz is in flat keys (or C) because of the horns - so if you find jazz depressing, than yes... I play mostly jazz and blues. As for Fb, that doesn't count - it's depressing simply because it's dumb.
@Tim - for some reason, guitarists always like sharps - is it because bending raises the pitch? A couple of weeks ago I was at a jam session and guitarist called out something in "C#" - I told him "you mean Db...." He look puzzled - I told him "it's easier" - he still looked puzzled... FYI, Albert King, a blues/RnB/Jazz guitarist (actually my favorite guitarist - top notch hardass musician - on one cut he gets pissed off at Steve Cropper for messing up a chord - and a genius on guitar) uses flat key names - a few times on records he call out keys to the band - always uses the flats.
@DavidBowling - Bb is supposed to "the most bluesy key", (maybe because it's a double "b" for blues...?) but I think maybe Fb would be even better. Besides the music being bluesy, so is the key signature. Monk has a tune called F Minor . Mingus has one called E's Flat Ah's Flat Too . You can have one called F Flat ! ( AKA -Flat Tire Blues )
@Stinkfoot - on guitar, it's always easier to sharpen a note, open strings too. Flattening is simple, go down a fret, but it becomes slightly more tricky to flatten an open string. The irony for me is that a lot of guitarists tune yo open Eb, which means when they play 'Blues in E, Blues in A', they're actually not...And I'm still pondering as to why Db is easier than C#. And actually only ONE will be correct for a given key. And - doesn't C# occur sooner in the circle of 5ths than Db - in key sigs at least?