Guitar

A good starting point: Justin Guitar has a great basic tutorial/tips on this matter:

• RT-001 • Beginners Recording Guide
• RT-002 • Audio Editing Software
• RT-003 • Audio Interface
• RT-004 • Microphone Guide
• RT-201 • Recording Acoustic Guitars
• RT-202 • Recording Electric Guitars

• How To Setup An Audio Interface At Home
• How To Set Recording Levels At Home
• How To Record Clean Tracks
• How To Record Vocals At Home
• Vocals: How To Record Music In A Home Closet 

• Re-amp technique (with latency turnaround): record your guitar with dry signal and try different sound effects later.
  One problem of doing this is that:
    a) you opt not to listen the sound effects while recording;
    b) you opt to listen the sound effects but you get latency;
  A turn around is discussed in this Guitar Player Magazine article: "The Recording guitarist - Re-Amping with DAWs", using an Y-cable too achieve something like this:
  
  
  Some people argument that the Y-cable reduces your guitar signal. But there are many ways for you too achieve the same thing (maybe your audio interface has dry line out? Using a active DI box? Using a passive DI box? ...?), so just try them out and see what works best for you.
• Using a Noise Gate (Reaper tutorial)

• A great tutorial/demo on how to correctly compare multiple microphones
  Microphone Comparison - A Tutorial - part 1 of 2
  Microphone Comparison - A Tutorial - part 2 of 2
  Keep in mind that louder mics always sound better, so you need carefully adjust the gain in each mic so you can compare them with valide information.
  "When comparing similar microphones for a given task, like the acoustic guitar recording demonstrated here, I think it's important to use the same performance, recorded simultaneously, with carefully matched levels. Without these precautions we're not really comparing the mics fairly.
  Part 1 demonstrates setting up the microphones and calibrating the mic preamplifier gain.
  Part 2, demonstrates a recording session, followed by a final round of gain adjustment, to create the matched clips for comparison."
• Audio Interface Comparison
• Studio Monitor Speaker Comparison
• Studio Vocal Mic Comparison (starts with a good explanation of the multiple kinds of mics)
• Setting Up Your Home Recording Studio
• MIDI Keyboard Controller Comparison

• Soundcard: is meant for games, play audio and movies, i.e. their main purpose is not to record audio, althought you can do it with them (a soundcard is also an audio interface).
• Audio Interface: this term is used to designate a special type of "soundcard" but wich main focus is to record and monitor sound. They allow (depending on the model) low latency, midi and audio inputs/outputs, better analog/digital and digital/analog conversion, etc.