There're a bunch of fascinating performance tradeoffs between B+ trees and LSM trees, which come out when you're choosing between something like MySQL InnoDB or PostGres (B+ tree) vs. LevelDB or Apache Cassandra (LSM trees). LSM trees tend to be faster for inserts and for write-heavy applications, and they offer very fast reads and writes for frequently-accessed data. They also depend upon the bandwidth of the disk rather than the seek time, and bandwidth has of late been increasing significantly faster than seek times. OTOH, they offer very variable latency, as an insert might trigger a major compaction, while B+ trees have a bounded latency limit. A lot of the distributed systems work at Google (a big user of LSM trees via BigTable) comes from the need to work around the poor 99th percentile latencies of LSM trees.
One useful data structure is the B+ tree http://en.wikipedia.org/wiki/B%2B_tree