The maximum possible speed in the Star Trek universe (not including the original series). Between the 23rd and 24th centuries, according the the Technical Manual, the warp curve was redrawn to be asymptotic, increasing sharply between Warp 9 and reaching infinity at Warp 10.

In other words, Warp 10 is unachievable by any means in the Star Trek universe. "Voyager" episodes that claim anything else are the result of crap writers who don't research their own material.

regarding the greater than warp 10 travel in All Good Things (TNG), I remember reading that the writers covered for that by proposing that in the future Starfleet reverts back to the old method of measuring warp speeds (ie. the one used in TOS) .. where warp 13 (or whatever) would actually equal warp 9.9293482385728345 or some such thing on the TNG scale (riiiggghht).

or it could've all been just some elaborate fantasy created by Q .. yes, in fact, that's what I'll use to explain all discrepancies in Star Trek episodes .. bwaha .. ha.

and for the sake of drama .. Babylon 5 makes me want to enter into a violent fit of MoJoe-ian Rage due to its blatent .. rip off-ness. ;)