For a protocol-aware logic analyzer I'll offer my own whole-hearted endorsement for the Saleae Logic series. I have an older Logic16 (pre-analog version) and it has saved me many times - easily paying for itself in terms of saved time and solved problems.
I'll also endorse the Total Phase protocol analyzers, but they are more application specific - more capable for dealing with large captures of specific protocols, but not as flexible for general purpose problem solving.
If I had to start over and could only afford one testing tool, I think that a new Logic with analog input would offer the most flexibility for the money.
-Bryan