ibisMail - Filtering Mail
Rolling out in a $3.99 iPhone version and a $7.99 iPad one, ibisMail bills itself on its strengths with creating and using filters as well as thread view of email conversations and a unified inbox. It also sports Dropbox integration and works with Gmail, iCloud, Yahoo, and other POP3, IMAP4, and SMTP servers. A bit pricy, ibisMail is the closest to matching Sparrow for loads of features.

Group Email
Or since you're stuck with the stock Mail.app supercharge it with Group Email ($4.99/Universal). Create group lists to send out batch emails and attach nearly anything. Apple's clunky procedure requires being in the app that has the attachment, but this app lets you attach documents, contacts, your current location, photos and videos, Dropbox documents (which really opens things up), or recorded audio from within the app. Nicely done.

iMailG
Strictly for Gmail accounts, iMailG is a settings filled wrapper for the webmail version of Gmail. There are an iPad version for $1.99 and an iPhone one (Free), though the iPhone version does have several in-app purchases to remove ads and to get various push notification ranges. Unlike the official Gmail, iMailG also supports multiple accounts.

iPriorityMail
If you're very in to staying on top of all your notifications, then iPriorityMail (Free) can be your one stop shop. Get notifications for Hotmail, Yahoo, MobileMe, AOL, Gmail, Twitter, Facebook LinkedIn, eBay, and then tons of customizable groups and individual alerts. Never miss that one message ever again.

Better Webmail
As email clients get better at mobilizing their webmail versions, Better Webmail ($1.99/Universal) is there to accommodate Gmail, Hotmail, Yahoo, and AOL users with slick, quick access to their sites. Passcode lock your accounts, set up multiples, add your custom email domain, and keep everything in one neat and tidy place.

Yahoo!
Speaking of Yahoo! it's a shame there isn't a native iPad app for accessing your Yahoo! account. Though you can easily jumbo-size the iPhone version (Free), it isn't the same as having a customized experience (or landscape use). Email loads fairly quickly and comes with links for news, a friends social bar to keep track of what your friends read, and access to other Yahoo! services.

mailPro
For Hotmail, MSN, and Windows Live emailers, there's mailPro ($1.99/iPhone) which is fast and includes the ability to send photo attachments and manage multiple accounts from Microsoft. Passcode lock and app badges keep your accounts safe and keep you up to date with how many emails you have to push through. Light on features, it nevertheless handles all your basic email needs with an easy UI.

Gmail
Okay, so the Gmail app (Free/Universal) is kinda a gimme here. With the Sparrow team being hoovered up, we anticipate some of what made Sparrow great showing up in this app's updates. We just wish it could stay open to other email providers like Sparrow did. Look for multiple accounts and account specific signatures and better filtering and gestures and everything else we've come to love about Sparrow. Hopefully.

Bonus #1.Mail app
.Mail from interface designer Tobias van Schneider has a clean look to it that we can't help feeling the same love we felt when we first saw Sparrow. Get this baby up on the Mac and then onto our iOS devices and we might just be able to enjoy email again. And Actionsteps? We're crushing hard.

Kickstarter darling,Mail Pilot has been in the works for what feels like forever, though they are in beta testing stages and claim the release will be here by summer's end. Called "ingenious" by David Pogue, we have high high hopes. While there are hopes to port the Mac version, we don't know how long we have to wait. The feature set looks promising, let's just hope this two man team can work it hard.