If you're only dealing with crossovers, then yes. Civil War is the next big Marvel crossover.
Decimation is felt through the entire x-line, and I guess it just depends on what characters/type of series you're looking for.
Personally, I cannot recommend X-Factor enough. Uncanny X-Men had some good times, but took a nosedive that it only now seems to be climbing out from. X-Men Legacy is another good book, probably the most loved out of all the current titles.
Again, if you're looking at just crossovers then it would be: Civil War --> Messiah Complex ---> Secret Invasion ---> Dark Reign/Utopia ---> Necrosha ---> Second Coming
If you're going that route, you should read X-Force and Cable to really keep up with the Necrosha and Second Coming stuff.