Separate phono preamplifiers are nothing new in audio but they were mostly confined to the professional sectors of the industry until the late 80's, by that time the Compact Disc had become the dominant force in audio playback and manufacturers facing the laws of diminishing returns often choose to discard the phono EQ section of their amplifiers or to use a cheap IC for the function resulting in somewhat less than ideal sound. This opened up a whole new market for good quality separate preamplifiers as those that still use their vinyl heavily simply have no option but to buy one.
But it should also be noted that buying a high quality phono stage is also an excellent way of upgrading your set-up without having to replace the amplifier, it can also be a good way of balancing your audio chain, those with overly warm valve amps can add a precise sounding preamp and conversely those having one of those damp sounding English amps can jazz up their LP playback by buying a valve stage or a sparkly Japanese one, etc. Note that if you are using a low output MC pickup you will either need a premap that specifically supports it, and be careful that it has enough gain and low enough impedance if your pickup is a low output one, alternatively get one of those fancy Moving coil preamplifiers as well. Also be aware that many of the cheaper valve based phono preams have a limited bass response, this is due to the limited open loop gain available and techniques used to rectify this often induce phase errors.
Aaron Made the legendary Phono Module between 1990 and 2002, this was one of the more expensive modules on the market and could be bought as a standalone model or as a variant that was powered by one of their amplifiers.
Antique Sound USA Although the company has officially ceased trading they still have a few units of the PP-1 valve based preamp left for sale, those are built n.b. , a user review of the kit version can be found here and more general reviews can be found here and here.
Audio Synthesis Made the ADEQ kit in the 90's, it was based on a design by Ben Duncan that was published in HFNRR in 1989, it's was considered to be rather good at the time and one avid user and fan of the unit has a homepage dedicated to the units including details on some mods.
EMT Studiotechnik Made a range of RIAA preamps, most if not all were made to fit into the frame of their turntables but will obviously be useable standalone (if a bit industrial in appearance). The 139 is a Mono valve based unit that would fit into the frames of the 927 and 930 and the 153st and the later 155st were stereo versions for the same frames.
Eymann Made a high quality stereo RIAA preamp that fitted into a EMT 927 or 930 frame, named Type A 152 it was available from the late 60's into the late 70's and by some considered superior to the EMT offerings.
FM Acoustics Replaced the Resolution Series 122 Precision Phono Linearizer/Preamplifier and the Resolution Series 222 Precision True Balanced Phono Linearizer/Preamplifier with MkII versions in 2002 or thereabouts, since they appear very similar to the current versions both visually and functionally, the company does not publish detailed technical specifications for the new models and I cannot afford any of their products, any comments on the differences between the original versions and the current MkII's would be pure speculation. You can find some information of the original versions along with a picture or two on this page. Note that the 222 does not come with a power supply, it meant do be driven by a FM 266 amp or a separate power supply such as the RS 202A.
Graham Slee Projects This company more or less specialises in making phono preamps and related products, they make 2 budget preamps the Gram amp 1 and Gram amp SE. The GA1 version does support MC but the SE does not otherwise they are identical. A slightly updated version of the GA1 is appropriately called Gram Amp 2 and is slightly more expensive than the older version and the company also produces a high end preamp called Era-Gold. For 78 Rpm enthusiast the company makes a version of the GA2 with EQ that better fits FFRR and other pre RIAA records, it's called Gramp Amp 78 and at the same price and specs as the GA2 has to be something of a bargain. Finally they make a more versatile unit for avid 78 collectors called Jazz Club that allows you to switch between differing Eq curves.
Gray Research Made a variety of phono equalisers/transformers for low impedance pickups, most of these were for transcription turntables and do not have the correct EQ for RIAA LP's but it's possible that units such as the 602C are usable, they do support LP playback in addition to transcription records but predate the RIAA standard (I am not sure how close the earlier AES LP standard was to RIAA).
Kinshaw Electronics Made 2 models of phono stages namely the Overture and the Perception, the Overture was a fairly cheap model but the more expensive Perception was quite well known and liked in it's day, it was available with a built in power supply and in a high end version that has a separate power supply. In the last couple of years it was produced there was also a SE version of it available, although there are a few years since the company stopped production they still do repairs and can upgrade Perception units to the SE specifiction.
Mares Designs Introduced the Connoisseur phonographic preamp in 1987, it was one of the most expensive models available in it's day and was unusual in that it had volume controls, it was meant as much to act as a preamplifier for a minimalist phono only audio system as a phono pre in itself, it's also unusual in that it's a partially PCB-less design, almost unheard of in modern designs. It was replaced in 92 by the Connosieur Model 2 which was a refinement of the original design that included improved parts and a Dual Mono configuration, got great reviews in the USA hi-fi press at it's introduction. The company has more information on their homepage on the Model 1 and Model 2.
Michell Engineering Made the Iso HR. phonostage in the 90's and discontinued it around the turn of the century, much beloved in the UK but not often seen outside it.
Neumann Made a range of valve based preamps in the 50's and 60's some of them are considered classics by now, the most famous one is probably the WV-2 rack model, it's so rare and sought after that is current price on the street is sometimes over € 8000 for a stereo pair (there were apparently a Mk1 and Mk2 of this model). More common are the SEV-2 and the SMB-2 stereo preamps, they are mostly identical except for the fact that the SMB has input transformers. They were made to be fitted into an EMT Studiotechnik frame such as the 930, but can of course be used independent from them.
PS Audio Made one of the first separate preamps to be sold to audiophiles rather than just to the broadcast industry, the company has more info on their history page.
Russco Electronics Made the Fidelity Master preamp in the 70's and possibly before and after that, as the unit was intended for use in radio stations it featured balanced outputs.
Shure Inc. They had a 2 channel preamp made in the 70's that would only mate with MM carts but had low and high output options to enable the use of the unit directly to tape recorders, the name was simply Stereo Preamplifier.
Thorens Made the MM 001 in the 90's, a fairly cheap but quite reasonable MM capable preamp.
Williams Hart Electronics The predecessors to the current models of preamps were introduced in late 1992 as the "Shunt Feedback" Pickup Preamp by Linsay Hood (yup this is all that's on the unit, there in no manufacturers marking at all). These were available in 2 versions, the budget K1500 model that featured IC's and could thus be battery driven and was sold as a kit only and the 1450 that was all discrete and needed a power supply that was sold separately as the1565, those 2 were available both as kits and fully built.