1) More than two gigs of storage.
2) Outstanding spam filtering.
3) Can use a regulat email client, and use POP to connect to the account.
4) Cyburbia doesn't allow registration from yahoo.com accounts for many reasons; bounces, spammers, disappearing accounts, and so on.
What sucks about Gmail? You really can't make your own folder hierarchy, unless you're using an email client and connecting to the Google server. The Web-based interface it automatically sorts messages into threads.
Another option is Walla (
http://mail.walla.com), which offers a 3 gig mailbox. However, it's not Firefox friendly. It's based in Israel, and your mail may be blocked to addresses with aggressive spam filtering; Israeli satellite companies provide service to Nigerian cybercafes, and it's the source of a lot of eBay fraud..