What components are recommended for entry level mountain bike?
Here's the short list of should haves in mostly descending order:


Coil or air sprung fork with rebound adjustment, minimum of 80mm travel. Specs any lower than this aren't actually meant for actual mountain biking. Maybe a little unpaved riding, but not mountain biking. Replacing a fork is expensive. Buy a bike with a fork as described and the subsequent parts listed here will almost certainly follow.
Double walled rims. Single walled rims suck and you will trash them. Double-walled rims are almost always stronger and longer lasting, and often lighter.
At least an 8 speed drivetrain. I'm just talking about the cassette (the rear gears). Multiply that with the 3 up front and you've got 24. This will give you decently tight gear ratios and keep you clear of the low quality parts that come in 7 speed configurations. If you're willing to spring for it, go 9 speed as much for the quality increase as anything else.
Mechanical disc brakes. You can get by with V-brakes, but a nice pair of mechanicals (typically Avid BB5's or BB7's) will make a world of difference in terms of modulation. A word of warning though, some entry level hydraulics are worse than decent mechanicals. Make sure you try them and make sure they stop you before you buy. All disc brakes require a good handful of hard stops to achieve maximum power, so keep that in mind as well when test riding.
Freehub rear wheel. Stronger and more durable than the older style thread on freewheel type hub.
Cranks with removable chainrings. Cheaper cranks have riveted on chainrings which means when the chainrings are worn out you have to toss the whole crank. That's lame.



Here's what not to get if you're looking for best bang for your buck in a beginner/intermediate package:


Anything full suspension. Just don't bother at the low price point unless you have a really good reason. You'll get way more bike if you stick with a hardtail.
Anything other than an aluminum or maybe steel frame. Aluminum is going to be the most common, steel usually disappears at the intermediate-ish price points, and then re-appears at high end price points. Aluminum is likely your ticket.
Anything from a department store or anything from a brand that also sells at department stores. The brands that have fallen from grace have been bought up by big conglomerates and prey upon people with brand name recognition, especially at lower price points. Avoid.