If you have the disk space you can create a new tablespace for rollback. Create new rollback segments and set an optimal size. If you are doing a lot of large DML transactions whichever rollback segment that is getting used will grow, without the use of the optimal parameter they will not shrink. You want to allocate enough rollback so that Oracle is not always dynamically creating rollback. You may want to make the rollback extent size larger. There are some tuning scripts that will tell you about the efficiency of your rollback sizing. If you average transactio take 5megs of rollback you may want to have 5 meg extent sizes.

This is an example of one of our rollback segments

create public rollback segment rb1
storage(initial 512K next 512K minextents 32
optimal 16M maxextents unlimited)
tablespace RBS;
alter rollback segment rb1 online;

You may want to make yours bigger if you are doing more dml. The real test when doing optimal sizing on rollback is how many times do they shrink. You want to keep that number low.