I always use the olly Asm/Disasm library in my VB6 projects.
took a peek around today to see what I could use for C# and ended up porting my VB6 code over so I could use Olehs engines from C#.
In other news I stumbled across SharpPCAP, and TCPRecon the other day. TCPRecon is a small project on CodeProject that does TCP stream reassembly. Both are pretty nice packages to have around.