I've been working on and riding mountain bikes for over 15 years now. While the glamorous high end stuff like Shimano XTR and SRAM X.O. garners all the headlines, its the mid-level equipment that most riders use. Over the years I have seen what works well and what doesn't. So here is a recommendation for affordable mid-level parts that I have used or use and endorse as being solid, reliable, and perform excellent.
Rock Shox Tora 318 Solo Air (Tora Race)-The motion control damper on this fork works right up there with my all time favorite Manitou TPC+ damper. It is very adjustable and does not suffer from spiking like some other Italian branded fork. The Solo Air cartridge is easy to adjust and is very reliable. The spring curve is just right to have plush at the top of the travel while ramping up at the bottom. The fork is very laterally stiff and easy to service.
SRAM X-7 Shifters and Rear Derailleur-Precise shifting in all weather conditions is this combo's claim to fame. It doesn't seem to matter what you throw at the X-7...it just keeps hitting its shifts perfectly.
Deore Front Derailleur-I love this cheap workhorse derailleur. Its performance is right on par with LX and XT front derailleurs I've owned, no reason to spend more to save a few grams.
Shimano and KMC chains-The Shimano HG73 chain, made by KMC, is another workhorse. Use a SRAM, Connex, or KMC quick link with it and it will not let you down. Another great chain in the same price range is the KMC X9. Both these chains use mushroomed center punched pins that have a pull strength that far exceeds SRAM PC chains.
Shimano HG61 Cassette-Not for use on aluminum freehub bodies (which I would never recommend anyway), reasonable weight and price and very long lasting. When combined with the recommended chains above, it shifts with pure precision. And the satin finish looks damn cool!
Shimano XT M756 Disc Hubs-Ok, you get your XT but at a bargain price. These hubs are absolute winners and reliable as it gets. Say what you will about cup and cone bearing systems, the races are precision ground for smooth as silk rotation. Easy to service, good seals, and reliable hubs...what else could you ask for at the price these run.
Cane Creek S3 Headsets (ZS3 included)-Good seals, light weight, long lasting...oh yea and under $50
WTB SpeedDisc Rims-They use a "shelf" with an extra lip to really lock in the tire bead. WTB refers to this as the International Bead Seat. What this means in real life is these rims are great for running tubeless conversions on with either the Ghetto tube method or the Gorilla Tape method. 9 months and 4 different tire brands and not one burp running tubeless.
Time Alium Pedals-The pedal you just can't kill. Immune to mud and snow, consistent entry and release, bomber construction, and a large platform so you can't miss clipping in.