Wow...

Going against the grain here...

Best:
My Mackie Onyx 400F I bought the CEntrance driver which solved the only issue I had. Mackie has recently released a very stable and complete update of the drivers. I am using the new drivers and it is great.

Sonar 6PE... my favorite! (from 2xl on)
ADL600 tube preamp. The most amazing preamp I've ever heard.
Neumann TLM49 A vocal mic for the ages.
My ASAT Z3 and ASAT Classic.... Leo to the bone!
Voxengo!!! The best VST plugs on the planet. He could sell them for much more then he does. In fact, I think the low price misleads some folks. They are incredibly deep programs.

While not the best ever, I did purchase Autotune 5. Quite frankly, it works without audible artifact. You simply can not tell it is working other than the vocal is in tune. A tremendous improvement from previous versions.


Worst...
My ADATS. I bought them new for around $7k. The next month, they were about 1/2 that price. They worked good but broke down about the same time Alesis went bankrupt. They sat in a repair shop in Dallas for almost a year because no parts were available. After they were finally fixed, I used them a couple of months and then went to the HD24 system.
I gave both of the ADATS away last month.

Best Purchases: SONAR (and I'm not being a "homer", I love this software), the Mackie Control Universal and extender (can't believe I've ever TRIED to mix with a mouse), the MOTU 2408mk3and 24IO, the Motif Rack and the Triton Studio. These pieces of gear are without a doubt the center piece of my studio.

Worst Purchases: Tascam US2400 control surface (I really should sue someone for that thing!!!), Alesis S4 (I think that's what it was called), Midisport 8x8 midi interface (wierd because the 2x2 works perfectly)

best; Waldorf Edition, Musicman Stingray, Sennheiser ME40/K3U SDC, Sonar 5/6 PE, Epiphone Valve Jr. head, TC Powercore,

Worst; Lexicon Core 2, Behringer ADA8000, any solidstate Ampeg, Cad dynamics, shure Beta 57, MOTU microlite parallel

Worst: Indonesian Squire Strat. Hate its guts.
Best: Presonus Firebox, M-Audio BX5s

Best : Mackie Control Universal, Mackie Onyx 400F (with the new drivers recently released), PodXt Pro, EzDrummer, Sonar, any of my Dean guitars, Washburn N4 guitar

Worst : Korg D1200 (hate the fact that Korg's multitrackers only have half the track-count when going 24bit), a couple of Gibson-guitars, Marshall Valvestate (both generations owned), Behringer mixer of some sort, Behringer Enhancer thing, a Peugeot 206 without aircon, DFH Superior

Stuff that's Ok, but not great, but not that bad bad either : Esi nEar06, AKG K240S, Maverick Custom F1 guitar

This is a great thread. Here are my best purchases:

Focusrite Liquid Mix, UAD 1, Sonar, EzDrummer (and DFHS I guess), Yamaha Motif, Taylor 510ce, Budda Superdrive 30, PRS SE Maple (awesome guitars for the $$), Neumann U87, Trident S-20, Yamaha I88x (for the pres not as an interface and it was a steal at 200 bucks), RNC compressor, ART Levlar, Apogee Rosetta.

Mistakes (for me anyway)- AT4040, Rode Nt2, UA solo 610 (great sound but I prefer the Trident on just about everything I throw at it so it's now collecting dust),

Best- My Brian Moore
Worst-toss up ART SGE or AKG C3000
Rj

Best

Martin X0001 so easy to play
Levinson Blade Strat Texas Pro Just wow
Focusrite Vocal Master - I think it helps!
Blue Dragonfly mic - sounds lovely
Ozone for mastering - lots of presets for the stupid like me
Yamaha DX7s - if  I hadn't bought a second hand one of these 18 years ago I would never have returned to making music

Worst

I hate to say this but
Gibson Les Paul Classic 1960 Reissue - cost a fortune and is so bloody heavy.  Blows the socks off everything with a Marshal amp but for me in the studio a silly luxury that is going to waste.  I find it hard to play too.
Joe Meek VC3 - maybe mine is broken as it doesn't seem to do anything!

I'm embarrassed about some of the bad decisions I've made, but here's my list: 

Best:  
Vocalist Workstation EX - I still love it. 
Studiologic SL880 - I love having 88 piano keys to play on. 
Mackie1402-VLZ - It was like hearing clean sounds for the first time. I only wish I would have spent more for the 1602. 
M-Audio Delta 44 - Old, yet still going strong. Glad M-Audio decided to make Windows 7 64-bit drivers for it. 

Worst:
Here's a story I've been wanting to get off my chest: "Roland Music Processing System (MPS)" was a very early DOS music sequencer. It wasn't too bad for those days, but then Roland announced a new product, "Mesa"). Naturally I wanted to upgrade to the new version, however, Roland would not give an upgrade price. You had to pay for it new even though I had the previous product. Back then (circa 1987) software was expensive and I didn't have a lot of money. I wrote them complaining that I should get an upgrade price on their new product since I already had MPS and they refused. I swore at that point that I would never buy any products from Roland.... and I haven't. I've had Moog, Ensoniq, Yamaha, Korg, Casio, Alesis, etc., but I would never even consider buying anything from Roland. I was already using Cakewalk when Roland bought Twelve Tone Music otherwise I would have never bought Cakewalk or Sonar. So there you have it. To make matters worse, I wound up buying Personal Composer and not long after I bought it, Jim Miller, the guy who developed it who lived in Hawaii stepped on a sea urchin and died. Following that, my brother who worked at a software business gave me a demo version of Cakewalk and I liked it and bought the full version and have been using and upgrading it ever since. BTW, "Mesa" failed miserably. Serves them right! 

DKI Synergy - Paid the price big time for being on the bleeding edge. I spent months writing BASIC software to try to control it with some success. 
Yamaha MD4 - a 4 track cassette recorder - nothing sounded good on it.  Sold it on eBay.
Yamaha TX81Z - It was a poor man's rack mount DX7, but I never really liked the sound of FM instruments and programming it was a pain. 
Elka String ensemble - Wouldn't stay in tune and in general sounded like crud.         
Wurlitzer Electric Piano - I know some people love these and many softsynths emulate the sound, but I think it sounded and played like crap.
A Getzen piccolo trumpet that never lived up to my expectations. 

Runners up: 
I had an old Micromoog I should have never sold since it was my first synth. Wish I still had it although I have a free Minimoog softsynth that sounds better.  I miss being able to twiddle the knobs on it. :)

Best: Sonar 7 PE, TC Electronic Impact Twin, Monkey Banana Turbo 6 Monitors, Vovox Cables
Worst: All from Behringer, Cubase SX, Studio Projects C1