|Class Name :
Radiation harvesting vessel 
|Unit Run :
1 built in total. 1 have been lost in all.
2374 , remained in service until 2374 
|Length : 5,000 m 
80,000,000 metric tons
|Defence Systems :
|Light Duranium / Tritanium Single hull.
Sub-impulse only :
|Capable of low sublight speeds only
Built by the Son'a for the singular purpose of harvesting metaphasic radiation from the ring system of the Ba'ku homeworld. 
The Collector was built in a Son'a system and then towed to the Ba'ku system in 2374. It was intended to be used as part of a conspiracy by the Son'a and the Federation Council which involved the forced relocation of the Ba'ku settlement to another planet followed by the "strip mining" of the rings. The collector would deploy a giant pair of folding panels and launch a small module into the rings to begin the collection process. 
The plot was discovered by Captain Jean Luc Picard and ultimately defeated by the crew of the Enterprise-D. Captain Picard succeeded in destroying the collector. 
|Star Trek : Insurrection
|Approximation, based on visual comparison of the Collector and the Enterprise-E in various scenes of 'Star Trek : Insurrection'. Star Trek : The Magazine gives a length of 1,254 metres, but this is only twice the length of the Enterprise-E; the scene of the collector's destruction as the Enterprise-E swoops over it makes it clear that the collector is in fact many times the starship's length.
The idea of the Collector being sub warp only is of course the major speculation here. There appear to be three possibilities for this ship; one, it was built on site in the Ba'ku home system and is not warp capable. Two, it was built somewhere else and is a warp capable ship that flew to the Ba'ku system under its own power. Or three, it was built somewhere else and towed to the Ba'ku system. It seems unlikely that the conspirators would go to all the trouble of building construction yards in the Ba'ku system just for this one ship, and it likewise seems to be to be a bit unlikely that the Son'a, who are barely in advance of the Federation, could build a 5 kilometre long warp ship. So building it elsewhere and towing it seems to be the most likely option to me. This is reinforced by the idea that the collector seems to have no crew of its own, or indeed anywhere a crew could be.