Can you be more specific? Do you need a specific kind of workload (I.e. NFS, CIFS, desktop, database server)? Do you need block level, file level, system call level?
If you find something freely available that is not present on iotta, you might also let Geoff Kuenning know so he can link to it. Iotta is intended to be a resource for just this sort of thing, and if it's missing stuff, then you can earn good will from the storage community by helping expand it.