I've got a thing for Calrec modules.
For the uninitiated, there are certain classic pieces of gear which appreciate in value over time. There may be a number of reasons: fashion, quality of manufacture, reliability, or a certain "quality" of being. Audio gear is no different. Amongst the hi-fi buffs, old Marantz and Dynaco amps, Linn turntables (among other items) and Quad electrostatic speakers are sought after because they are classic designs and sound good. (You do have to wonder about hi-fi fans' claims, though, when they start talking about the sound of cables. If only they knew how many pieces of wire, electronic components, and connectors their favourite recordings had been through on their way to... insert hi-fi format of choice here!)
For professional audio engineers there are a few names to watch out for: Neve, API, Pultec, Fairchild, Teletronix and Urei. (There are of course others.) In particular, certain microphone pre-amps -- sometimes combined with equalisers (filters giving tonal control) -- have a certain quality widely recognised for endowing audio signals with a distinctive "colour". Some compressors too. Many of these are components which were originally part of mixing consoles.
Rupert Neve's classic designs are good examples. The consoles produced in the late 1970s and early 1980s were modular with different functions being performed by modules that plugged into a frame. Neve's mic and line amps and EQs are sometimes now more valuable than complete consoles whence they came. That may be changing now as there are fewer and fewer of these consoles, but in the last 20 years a number of owners realised that they could make more money selling individual modules than the complete console and so there are a lot of them around. The problem is that most of them are racked up and in working studios and it's hard and very expensive to get hold of them.
Certain manufacturers and models attract more attention than others. So one sometimes finds lesser-known units that may be just as high quality. Calrec is one such example. As I understand it, they started as an "audio" club and manufactured some BBC-designed equipment. When Neve couldn't fulfil all the orders, the Beeb turned to companies like Calrec. Some of the Calrec modules are considered to be as good as Neve 1073s or 1084s but are not as expensive. (They are becoming better known.)
Hard-up engineers like me are always on the look-out for bargains. Over the years I've picked up a few: an Aphex 622 expander/gate for 30% of the retail price, some Audix mics for a song, a Yamaha SPX990 for much less than the typical second-hand price at the time. Other items may be inexpensive but are surprisingly good. The early Behringer compressors are, in their functionality and response if not their actual sound, a knock-off of a dbx 160. They actually use THAT Corporation VCAs. I've heard a story that Joe Malone of JLM Audio buys Behringers by the bucket-load because he can't buy THAT VCAs for anywhere near as cheaply. Anyway, the late-model Behringers feel very flimsy (you could balance them on one finger without any discomfort, but, as with any potentially controversial claim on the internet, I'll say that Your Mileage May Vary!). The early ones are built like battleships. OK, the non-adjustable attack and release times on the limiter section make the latter unusable but the compressor section works just as you expect it to and it sounds all right.
Well, I've been hitting ebay too much for my own good lately. I picked up a Lexicon PCM60 reverb unit (c.1984). No, it doesn't sound like the Concertgebouw in Amsterdam. You can now buy software that does! The boffins have actually measured great rooms and modelled them in the reverb algorithms. The Lex isn't realistic and it's very simple, but it sounds good and a little funky.
I also got 4 Calrec modules from a guy in Oregon. They come out of a Calrec Compact console and include a mic pre, 3-band EQ plus switchable-frequency high-pass and low-pass filters, and 4 auxiliary sends. Unlike the larger consoles, almost all the channel strip functions are in the one module. I thought to myself: if the gear is in good condition, how bad can it be? So I took a punt and bought four, even though they're not the better-known modules. I'd like to get them racked up in pairs and sell one pair to offset the cost.

Just lately, someone was selling a DL1656 compressor. This is better known. And then a crowd in Northern Ireland was selling two PQ1347 mic pres and EQs. Mixmasters in Adelaide is selling a racked pair of an earlier version of the same for $3500. Maybe that's too high because they've been listed for quite a while now. But I think I got a bargain.
So bit by bit I'd like to get them racked and keep some and sell some. I may not make any sort of profit but if I can substantially offset the original purchase price and racking cost, I'll have a few nice mic pres and be happy.