windbg (or kd--console version) is pretty good imo, especially if you use livekd. The notable advantage is wndbg's native support of M$ symbols, therefore making it so much easier for kernel debugging. kd has some really good commands that makes it very easy to explore windows internals, data structures, functions, exports, etc. And they are free!

If you cannot afford softice, livekd+wndbg is the way to go for kernel level debugging. for ring3 debugging, olly is very good.