Here are some possible tips:

http://mindprod.com/projects/projects.html

other tips are standard business systems, like simplified
- customer order system
- invoice system

etc with web interfaces, databases, and so on. Just add some
functionality, to be able to use some technology (it might not be
relevant in that actual case but then again you are not making a real
system are you.) E.g. why do you use transactions? because some
operation can not be performed atomically across several systems without
using... transactions, so create some operation that does require access
to several systems( for example across several DBs) and so on.

tom