Most of the classic 'easy solos' have already been mentioned, but I think we're omitting the obligatory first song; Smoke on the Water
It was most of our first riff, you may as well see it through.
Thing I find though, with melodic riffs, is... well two things I find are a) Because they're a personal stamp on a song, it's quite hard to really 'learn' it, regardless of technical difficulty, and b) again, because of the emotive quality, your favourites are always easier.
To summarise, pick a solo you love and work at it.