At the bottom of the page, next to Gmail view, choose standard without chat instead of standard with chat. Use the standalone google talk client or a client like Adium instead.
Disable Web Clips
In Settings > Web Clips uncheck Show my web clips above the Inbox.
In Settings > General choose No snippets - Show subject only.
Tweak Better Gmail
If you use the Better Gmail Firefox extension, disable any of the features you're not using by going to Tools > Addons > Better Gmail > Preferences. I basically just use the extra keyboard macros and disable all the other features.
By far the best performance increase comes from using standard without chat version of gmail instead of the full chat version. Tweaking Better Gmail also makes a noticeable difference in speed. I'm not sure if disabling web clips and snippets actually makes gmail faster, or whether I just think disabling this stuff makes it faster. In any case, I'm keeping this stuff disabled because it seems to work. Furthermore, disabling this junk removes a lot of clutter and distraction. Web clips just steal my attention away from the inbox or email I'm reading and snippets make the inbox look really messy. Without this junk I'm much more focused on my emails.
Gmail is still a little too slow for me. I may try setting up pine with pop access or building a little as3/flash/air app for quick message composition. Further reading: gmail vs pine