What are some songs that have really nice solos or riffs?

Most I Know:

Sweet Child O' Mine
Welcome to the Jungle
Paradise City
November Rain
Godfather Theme
Hells Bells
Back in Black
Sunshine of Your Love
Stairway to Heaven
Smoke On The Water
Fender Stratocaster Highway One
Digitech GNX 4
Laney Lx65R
Purple Haze, almost every guitar player knows at least the intro.
Xbox Live GT: IX Michael IX
Moonspell - Everything Invaded
Septic Flesh - Brotherhood of the Fallen Knights
Tiamat - To Have and Have Not (Live version with Fredrick Akesson)
Ayreon - The Shooting Company of Captain Frans B. Cocq

Hope this helps!
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Warmoth Strat w/ Lace Holy Grails
'07 Roadhouse Strat
Washburn WD-21 all Koa Acoustic
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Bugera V-5
Cult of Personality by Living Colour.

Almost any Led Zeppelin or Black Sabbath riff is a good riff/solo. Cream is really good with their stuff too.
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Boss DD-6
White Room by Cream.
Manic Depression, All Along The Watchtower, Little Wing, Castles Made of Sand, Voodoo Child (Slight Return), by The Jimi Hendrix Experience
Day Tripper, Helter Skelter, While My Guitar Gently Weeps by the Beatles
Peace Frog, Break On Through (To The Other Side) by The Doors
Welcome Home, The Suffering by Coheed and Cambria
Layla, Bell Bottom Blues by Derek and The Dominos
Cocaine, Bad Love, Pretending, by Eric Clapton
Gravity by John Mayer

And alot more.
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Quote by parigod
Purple Haze, almost every guitar player knows at least the intro.

I'd add Foxey Lady and Manic Depression to the list, too. These are great tunes to learn and jam.