There's the Hipshot Drop D tuning machine that makes dropping the "E" to "D" easy, but I recall another de- tuning gadget that was much easier to use and much, much faster. Sorry, can't remember the name of it. I saw a Drop D tuning gadget on a dog house (orchestral or stand-up) bass once, too.
I've been debating on getting a Hipshot, because it detunes at the peg. There's another detuner that works at the bridge (the EVH D-Tuna, apparently created by Eddie Van Halen), as well as one that clips directly on the string just above the nut (the Pitchkey).
The D-Tuna has a problem with Floyd Rose tremolo bars, but that's not really an issue for bass. It also has a problem with floating bridges in general, although this isn't a problem for me. Detuning at the bridge, though, just strikes me as asking for problems. That said, it seems that most of the people that use them are quite happy with them.
The Hipshot on the other hand can be a bit fiddly to install and get working correctly. In some cases you may have to do a little work on the nut to get the string moving in the nut freely. Again, most of the people that use them seem to be quite happy with them.
The Pitchkey seems to be the most problem-free of the bunch in terms of installation. Since it also tunes behind the nut, it can suffer from the same string movement issues as the Hipshot. My biggest concern with it is that it 'pinches' the string, so I'm concerned that it can cause extra abuse to the string. Dunno if that's a legitimate concern or not.
Have you seen a fanned fret bass guitar? Their intonation is much more accurate than a standard fretted bass. They look like a difficult transition would be required. Naturally the player in the ad said it was easy as pie for him!
I just ran across those the other day, first I'd heard about them. I've not had a chance to play one, so I can't say much about them, but the concept seems reasonable enough, and one thing I've noticed on my bass is that there is a very slight intonation change at the 12th fret. I don't play much up there, but it bugs me knowing that it's there and I can't really do anything about it.