To answer your question we would need to know what it is you need to or would like to achieve with these tools. Personally I have evaluated quite a few in the 5 or so years that I have been a DBA and have not found many that perform much more that Enterprise Manager, Query Analyzer, Profiler and Perfmon already do. These allow me to do anything that needs to be done on our failover clustered, replicating and full text enabled db's.
That being said, we do use three other programs here: Embarcadero's DBArtisan (nothing more than a few of the tools already mentioned in a different GUI), Lumigent's Log Explorer (reads the transaction logs and allows you to undo bad things, I retrieved a proc I accidentally deleted a few days ago with it) and Imceda's/Quest's Speed Coefficient. There is another I looked at a while ago named DB Scanner from Internet Security Systems. At the time I was impressed but budget bound. It was good then and I will be looking into it again soon.
My suggestion would have to be save your money unless you need an elaborate design tool such as ERWin or one of the above programs we use and invest in few good books.