I tend to use 640x480 for my pictures; fits in most folks' browser windows and makes for a decently quick download. For my albums, I use a tool called Porta; I select the pictures I want to post, and it generates an album page that uses either a Flash viewer or straight HTML-javascript, and also reduces the photo size accordingly. Here's a sample:
[
glenn.pulpitrock.net]
I like NDHolmes' approach on [
drgw.net]; displays a thumbnail with links to various sizes from 640x480 to 3888x2592 (danged Canon 10MP DSLRs... :-)