Go Launcher EX (free)
ADW Launcher (free, EX version has a few extra features, paid)
Launcher Pro (free, paid version also available)
Zeam Launcher (free)
There are a number of other more specialised launchers around too, like Espier Launcher which mimics the iPhone. Of the ones listed, ADW Launcher is probably the most versatile (though I haven't used Launcher Pro so it may be more so), Go is the most polished/smoothest and Zeam is the lightest weight.
Beautiful Widgets (paid)
Minimalist Text (free)
All three of these apps are widget based and extremely customisable. mClock and Minimalist Text also have facilities for loading configs, so you can find a lot of prebuilt themes for them floating around.
Opera Mobile (free)
Opera Mini (free)
Opera Mobile gives you a full web experience and is recommended for use when you're on wifi. Mini uses some Opera magic to greatly compress webpages and usually directs you to a sites mobile version and is therefore recommended for browsing when you're using mobile internet.
Camera Zoom FX (paid)
FxCamera is the Android equivalent of Hipstamatic, CZFX is the best camera app on android and Pano takes great panorama shots.
Barcode Scanner (free) - great QR code reading app, handy if you download things from XDA regularly.
WidgetLocker (paid) - Lockscreen replacement, very versatile, many, many themes available.
Calendar Pad (free) - ugly but extremely functional calendar.
Jorte (free) - another full featured calendar that's slightly prettier than Calendar Pad but less intuitive.
Dropbox (free) - cloud syncing and storage.
Dictionary.com (free) - Neat little dictionary app.
Epistle (free) - extremely simple plaintext note taking app that can sync to Dropbox.
G-Mon (free) - great Wardriving app.
Google Chrome To Phone (free) - Chrome users only. Send links from your desktop browser to your phone over wifi or data, super handy.
Google Translate (free) - Nifty as fuck.
HandyCalc (free) - The best scientific calculator app on android imo.
Tick! (free) - really simple rotary timer.
SwiftKey X (paid) - Keyboard replacement. I prefer Swype over it, but loads of users swear by Swiftkey's uncanny predictive text.