I have a Lytequest Apollo...which plenty of other manufacturers make versions of now. (or is it just one place making them, with 20 different badges for other manufacturers)
The Apollo is a large (15inch across approx) black metal sphere with a 300watt lamp inside and about 50 x 1.5 inch lenses randomly coloured, spread out over the surface. The whole thing rotates at a graceful 6rpm (again approx). The lamp life is quite amazing, I've had the unit a year now and its on its original bulb. I tend to use it during slowies and during certain 70's tunes, since the effect that it gives off is very 70's... I guess I give it about 30 minutes of use every wedding. I've seen these around now for about £55 each.
I also use a 4 channel lighting controller on a dimmer pack, which offers me a crossfade mode (channel 1 gently fades down as channel 2 fades up etc...etc...). The controller (an NJD Logic 8000LV) has a really good speed control in the lower ranges...the slowest gives each channel about 20 seconds before fading the next channel up. The 2 x overhead spotbank (16 x 60 watt reflectors in each) are run at 10% brightness, just idling through some patterns.
I've paid quite close attention to "Slowie" lighting, as it also comes in handy for "Atmosphere" or "Scene Setting" for that all important "moment of truth"....the bit AFTER you're up & running, as the guests are slowly wandering in ("Oh look a Disco") but before the main dancing starts. Similarly, I do a lot of dinner dances, so having something that allows the disco lighting to subtlely enhance/replace a halls cold white lighting, is a benefit too.
Other lights that I'm considering for slowies and atmosphere creating, are the upmarket versions of the old "Oil mix wheels", Kaleidascope projectors, and those "Aqua" style projectors that shine a "stargate" type watery effect onto a wall, in 4 slowly changing colours. I would LOVE to get one of those Antari ICE low fog machines...that create a 1 foot high carpet of fog on the floor, but Im too worried about the smoke warming up and rising up to the smoke sensors....
For slowies....avoid FAST rotating barrel effects...strobes (I kid you not...I've seen it done...and it wasnt pretty), Ye olde' worlde' Tandy 4 spot banks..(1,2,3,4, 1,2,3,4, 1,2...)