My favourite preamp of all time, from the ones below, is without question the Trace Elliot GP12SMX. I'd have one again in a heartbeat, especially if I could pair it with another lightweight 1U power amp like the Soundtech. I bet that combination would sound incredible through my current BF cab.
15w amp built at school + homemade (by someone) 1x15 cab (the least said about this, the better)
Phoenix PHA-1 hybrid 100w amp + Custom Sound 4x12" cab (the amp was, errm, quirky cab weighed a ton)
Laney Pro-Bass 150w 4x10 combo (my amazing parents bought me this for my 21st)
Carlsbro Delta 300w amp + 1x15 and 2x8 cabs (a bit underwhelming to be honest)
Trace Elliot GP12SMX preamp & Citronic 600w power amp (later replaced with Soundtech 800w power amp) + two Peavey 4x10s (my favourite ever preamp, but two 4x10s?? what was I thinking?)
Same pre & power amp + SWR Triad 1x15+1x10+HF (the best sounding cab I have ever owned, but oh so heavy and a bit quiet -- used with one channel of the power amp)
Euphonic Audio iAmp350 combo (I took the amp out of the combo and used it with the SWR cab -- a great amp, quirky eq but some good sounds available)
Eden WT400 amp + same cab (I borrowed Kiwi's Ken Smith 5 for a gig, it absolutely loved this amp -- a match made from heaven, the sound was to die for)
Same amp + Nemesis 1x15 & 2x10 cabs (lovely light cabs, sounded fabulous, but I wasn't quite happy -- after reading the 'same size drivers' debate I straight-swapped the 2x10...)
Same amp + two Nemesis 1x15 cabs (...for another 1x15 -- at last, this was a great sounding rig. The Nemesis cabs were always vastly underrated, I thought)
SWR SM-900 + same cabs (the SM-900 was an itch I just had to scratch, as used by some of my favourite bassists -- it came up at an irresistable price and I had to give it a go only a fleeting affair but it sounded sublime... had to be very careful with how hard I pushed it though. Very heavy unfortunately, so it had to go)
Genz-Benz Shuttle 6.0 + same cabs (thought I'd dip a toe in the Class D waters and was amazed at the sound this wee box made -- and my back loved me again! at last a properly lightweight rig)
Same amp + EBS Neo 212 2x12 cab (even lighter -- all the oomph of both Nemesis cabs from one box. Started a new love affair with 12" drivers)
Genz-Benz Shuttle 9.2 + Barefaced Super 12T 2x12 cab (my current rig -- louder than god shouting! The highs are less glassy than the EBS cab, but that's fine, I'm not after glass-shattering top end anyway)