Continuing with instruments such as you might use in a rock band.
There are some nice options for free acoustic guitar. Definitely check out the first three listings as this will give you a five very nice guitars.
Pettinhouse is the best place for free Kontakt guitars . He has two lovely acoustic guitars, the Classic Guitar and the Acoustic Guitar.
Flame Studios (Giga & SF2) has a wide variety of guitars including a Seagull and a Washburn acoustic. If you prefer Kontakt here are the bigcat versions.
Natural Concert Guitar (SFZ) or the bigcat version (Kontakt)
Ultimate Guitar Kit 2 or here (SF2) from the guy who owns orange tree samples now
Quartertone Guitar (Kontakt)
Project 16 Sherwood Guitar (Kontakt)
Spicy Guitar (VSTi)
Indiginus Free Guitar pack (Kontakt) includes the Double Tracked Acoustic Guitar.
Revitar 2 (VSTi) (Acoustic, Electric and Bass)
MSLP Lil' Nylon (Kontakt)
The free electric guitar options are staggering. Pettinhouse is wonderful, Flamestudios has a very nice collection, KMG7 is an amazing instrument and the Hephaestus guitar is very nice indeed.
Pettinhouse (Kontakt) also has lovely electric guitars, the Direct Guitar 2, the Warm Jazz and the Humbucker.
Flame Studios (Giga & SF2) has a whopping eight electrics including Fender Jags and Telecasters and Gibson Les Pauls. I converted three over to Kontakt.
KMG7 (Kontakt) is a brilliant 2 gig 'backing metal guitar library'
Hephaestus Clean Guitar (Kontakt) is a wonderful instrument.
Emily Guitar (SFZ) and bigcat version (Kontakt)
Jackson EMG (Kontakt)
Waves Factory Power Guitars (Kontakt)
Thrash DI Guitar (Kontakt)
DSK Electrik GuitarZ (VSTi)
DVS Guitar (VSTi)
NoiseCrux Peavey Predator electric guitar (SFZ)
Les Paul SG Custom (VSTi)
Suburban Guitarist (VSTi)
Oddities and Chords
Epic Guitar (Kontakt)
Bowed Guitar (Kontakt)
Tiple (Kontakt) lightly sampled guitar like instrument from Columbia.
MSLP Acoustic and Electric Guitar Chords (Kontakt)
Oderions Guitar Steel Chords (SFZ)
DIY Philharmonic Guitar (Kontakt) a wrapper for the Philharmonia guitar samples.
Guitar Rig Free