Systemtap is designed to solve the same sort of problems as dtrace, and has a similar user interface – the user writes small scripts which attach actions to named probes.
It is said to be unstable, it’s not usually compiled into your kernel by default, but once I got it working I didn’t have any problems.
You can see how it compares to dtrace in this table on the systemtap website (May be partisan 🙂
Dtrace has been partly ported to Linux by Paul Fox, an enthusiast, and is available for download for you to try – check out the links on his blog.
It has been said that kprobes are a dtrace replacement, but I’ve never tried them.