Well, if Red Hot Chilli Pepper solos are where you're at, maybe the next step is something in the ballpark of Pink Floyd's 'Comfortably Numb' - it's a nice solo too in my opinion. Some of the stuff by GNR too - or maybe metallica if you want something heavier. Depends where you are for technique - as I recall the californication solo isn't too tricky.

Best advice I can give is to learn the solo to a song you really love - doesn't matter how difficult it is, if you want it enough you'll get there.

Not a solo, but the piece I learnt that most improved my technique would have been 'Eugene's Trick Bag' - it's not for the faint hearted though! Sounds quite good even if not played at full speed and would help you develop sweeping & alternate picking. It also features diminished runs that I wasn't familiar with until I started looking at it...