In this continuing series here on ReadWriteWeb, we round up some of our favorite new applications for smartphones each month, specifically for iPhone and Android devices. This spring edition includes some major new launches on Android, like Netflix and Google Music, as well as some incredible technology leaps on iPhone, like the app which identifies trees by their leaves! As a bonus for this month, we've added a section with notable app updates and another featuring new tablet apps.

New Apps for iPhone

LeafSnap: Possibly the most ground-breaking app released in recent days, LeafSnap lets you identify trees by taking a picture of their leaves. Created by researchers at Columbia University, University of Maryland and the Smithsonian Institute, the app is like something you would see on TV, roll your eyes at and scoff, "as if that exists!" Well, technology moves fast - it exists! And, according to the app's description, this is only the first in a series of field guides the researchers are developing. (Free, iTunes)

Seamless: This app lets you start playing a song on your Mac then "seamlessly" transition to listening to it on your iPhone/iPod Touch, or vice versa. Both devices have to be on the same Wi-Fi network. ($1.99, iTunes)

FavFriends: A new way to keep up with your favorite Facebook friends, using a combination of a customized friend list and push notifications. Our coverage. ($0.99, iTunes)

Hype Machine Radio: A new app from MP3 blog aggregator Hype Machine lets you find new music from undiscovered, indie artists and stream to your mobile device. Our coverage. ($2.99, iTunes)

Voice Brief - Lite: Get briefed on your schedule, news, Facebook, Twitter, Google Reader, stocks and more, with this virtual assistant app that reads aloud to you. (Free, iTunes)

Yahoo Messenger: This new IM app for iPhone and iPad can do video and voice calls, text chat, presence, SMS and photo-sharing. Our coverage. (Free, iTunes)

Trover: A great local discovery app that offers photo-sharing, social networking and more. (Free, iTunes)

DOL - Timesheet: From the Dept. of Labor, this app lets employees track the hours they work and calculate the amount owed by the employer to verify they're being paid what they're due. (Free, iTunes)

i3D: This concept application tracks a user's head movement using the iPhone or iPad and updates a 3D scene on the device accordingly. A cool technology demo. (Free, iTunes; image credit AppAdvice)

do@ (doat) mobile search: It's hard to Google the name of this app, which aims to revolutionize mobile search. The idea here is one of a universal search app that finds movies, music, TV, shopping, news, people, sports, cooking and other information from one interface. (Free, iTunes)

Sonar: This new app helps you find the most relevant people in a room based on your Facebook, Foursquare and Twitter social networks. (Free, iTunes)

Meporter: A location-based news app for citizen journalism, this app lets you write, take photos or video and then share that info with anyone who has a mobile phone. (Free, iTunes)

Tracks: A new mobile photo-sharing app for private sharing between family and friends. (Free, iTunes)

Mixcloud: Now on iPhone, this on-demand radio platform provides streaming podcasts, DJ mixes and radio shows. (Free, iTunes)

ooVoo Mobile: This video calling platform is now available on iOS, in addition to Android and the desktop. Supports up to 6 parties at once. (Free, iTunes)

Songkick: This new app for iPhone lets you track 100,000 concerts and your favorite bands. (Free, iTunes)

iWork: Apple's own Keynote, Numbers and Pages have now come to the iPhone. ($9.99 each, iTunes)

New Apps for Android

Netflix: At last, on Android! Need we say more? Select phones only, but more are coming soon. (Free, Android Market)

Google Music: One of the biggest new launches on Android is Google's own Google Music app. This player app lets you access your MP3's stored in the "cloud" right on your Android phone. (Free, Android Market)

Goodreads: The social book discovery and sharing site Goodreads is now available as an Android application with access to almost all core features available on the desktop version. (Free, Android Market)

SPB Shell 3D: A new homescreen replacement/launcher app which is "gorgeous," "smooth" and "incredible," according to gadget review blogs. Works better on high-end handsets. Pricey, but cool. ($14.95, Android Market)

Regina 3D Launcher: Another new homescreen replacement/launcher app which works well on modern, powerful devices, offering 3D graphics, effects and new widgets. (Free, Android Market)

White House: The official White House application is now available for Android, in addition to iPhone. (Free, Android Market)

Hacker's Keyboard: For advanced users, this new keyboard is designed for use with SSH and features keys like Tab, Ctrl, Alt, Esc and Arrow Keys. (Free, Android Market)

ShakeCall: This fun Android app lets you answer incoming phone calls by shaking your phone. (Free, Android Market)

Spiceworks: I.T. management SaaS and community app is now available on Android. Our coverage. (Free, Android Market)

Bonus: Awesome Updates!

Wordpress: The popular blogging platform gets a major upgrade with tons of bug fixes and new features like "quick photo" posting, localization, mobile stats and more. Our coverage. (Free, iTunes)

Cardcloud: The app that promises to do away with business cards now integrates with LinkedIn, allowing you to turn your LinkedIn profile into your business card. Our coverage. (Free, iTunes)

Firefox for Android: The latest update brings the "Do Not Track" feature to the Android version of the popular Web browser. (Free, Android Market)

Seesmic: The popular third-party Facebook, Twitter and social networking app added support for Instagram and Salesforce in its most recent update. Our coverage. (Free, iTunes)

SkyGrid: This powerful news app was just updated to version 2.0, allowing you to follow topics you're interested in. (Free, iTunes)

Newsy: With the recent update, this news aggregator helps you keep up with daily news and video from multiple sources. (Free, iTunes)

Bonus: New Tablet Apps!

Photoshop Companion Apps: Adobe launched its trio of Photoshop companion apps for the iPad including Color Lava (a color mixer, swatch & theme creator), Nav (a touch control pad for Photoshop) and Eazel (for paintings). ($2.99, $1.99, $4.99, respectively, iTunes)

Plizy: Like April's ShowYou app, Plizy brings video recommendations from your friends to the iPad, but it also pulls in recommendations from other sources, like Twitter and your own viewing history. (Free, iTunes)

Fanhattan: This new app helps you find movies and TV shows from Netflix, iTunes and Hulu Plus, sort of like a TV Guide for the iPad. (Free, iTunes)

Watchlater: This iPad app lets you save videos via browser bookmarklets for later viewing. ($2.99, iTunes)

Games for Cats: Cat lovers, you have to try this! (and tell me if it works - I'm a dog person). A new trio of apps designed for cats comes to you courtesy of Friskies, the cat food company. (All free, Web - designed for tablets)

Remember the Milk: The popular to-do list application is now available on iPad, offering gesture support, syncing, notes, and other smart features. (Free, iTunes)

Google Earth: An update to the Google Earth for Android app brings satellite imagery and 3D building to Honeycomb tablets. (Free, Android Market)

Decks: A trio of apps for iPad, Decks for Apps, Decks for Movies and Decks for Flickr, these apps let  you discover new content matching your interests. Our coverage. (All free, iTunes)

SnagFilms: Watch free, award-winning documentaries on your iPad. (Free, iTunes)

iSwifter: This iPad app lets you play Flash-based games on the Flash-free iPad. Our coverage. (free 7-day trial, then $4.99/month)

That's all we have so far, let us know which ones we missed!