the quest for a perfect mail client

as anyone who uses email a lot can relate, it's hard to find a really good mail client. maybe i'm too picky, or too quirky, or too something. but i just can't seem to find a mail client that really suits all of my needs. i posted a while back about the things I like about thunderbird, and it's still mostly true. but, i'm still not quite happy - in fact, i've gone back to using Mail.app on my powerbook. Why? well here are the top couple things that have been driving me crazy with thunderbird:

• no search or filter on flagged messages. i can't believe that this hasn't been addressed! actually the one mail client that seems to have this right is evolution, which lets you save a search for flagged messages. maybe my workflow is wrong. but i use IMAP mail exclusively and when I get new messages that require action, I flag them.
• on that note, am i crazy since i can't find a keybinding in thunderbird to flag a message? i mean even mail.app has that.
• no on the fly spell checking. it's a minor nit, but it does get old. when sending work emails, i like to avoid nasty spelling mistakes, but having to run through each misspelled word (especially when my email routinely refers to "bryght" or "drupal") can be a pain. my eyes are pretty good at ignoring red squiggles that don't apply.

So, for now, i've switched to Mail.app on my powerbook as my primary mail app. I know, it doesn't satisfy the flagged message thing - although i saw a preview image of tiger's mail.app : which promises to have "smart folders" for things like flagged messages. that would be awesome. plus, mail.app comes with the nice features of - a) showing address book images with messages (the power of images - behold!) - for that matter, address book integration in general. the linux world should take note of simple, specialized applications that then work well with each other. b) the unread message count in the dock is great.

but, mail.app isn't perfect. it will start to bug me again soon, i'm sure. so what do other people use for mail?