Tweaking Apps:
ROM Toolbox Pro (seriously, the BEST combination of useful root tweaking apps ever)
Android Assistant (has a bunch of useful features like an auto task killer you can configure, battery use info, tons of real-time system info and such), Juice Defender (best battery saving app ever, I have plus and its great),
Standard Apps:
Google Currents (awesome free magazine and newspaper provider), Dolphin Browser (best android web-broswer IMO), FriendCaster (runs WAY lighter than factory facebook app and has more options), Sense Analog Clock (combination Clock, system info, weather and a few more options widget, TONS of stuff in one light very cool looking widget), Smart Keyboard Pro (best keyboard IMO, tons of options, skins, T9, compact, regular and other keyboards with a good dictionary and plenty of customization), Swiss Army App (a BUNCH of cool gadgets in one app, flashlight, bubble levels, rulers and more),
Free Games:
Cartoon Wars (there are a bunch, I like them all), Duke Nukem (free, no ads, AND its one of the greatest PC games ever to be released, come on, who doesnt like Duke?), GameBoid (FREE no ads game boy advance emulator, just download a BIOS file and whatever ROMS you like, runs FLAWLESS), Gun Bros (fun top down shooter game with single, co-op and VS modes), Zenonia 3 and 4 (BEST RPGs for android, period), Plants War (fun and cute DOTA style game), Veggie Samurai (the single reason my friend bought an Ipod touch, UNBELIEVABLY fun game, and no ads only costs $.99)
Paid Games:
Worms (who doesnt like Worms?), Star Traders (Hella fun space-captain RPG, play as a trader, pirate, military captain, smuggler or whatever you want, theres a free version, but $1.99 gets you like 10X the game), Gem Miner 2 (simple and addictive mining game), Death Worm, Draw Slasher (VERY fun strange swiping game, your a ninja monkey killing pirate monkey zombies, GREAT art and graphics)
Widgets:
LG Memo Widget (the ONLY memo widget which lets you write and view memos from the widget and without opening an app, if you want it PM me and Ill send it to you, since I got it off my old LG Optimus M and you cant get it anywhere else), GoSMS Pro Widget (GoSMS is AWESOME but if you want to just keep your regular SMS app you can download the widget separate and view, reply and do much more directly from your home screen), Power Control (TONS of "power" buttons to choose from in a simple and customizable widget, WAY more functionality than the factory status bar power widget)
Theres a good starting list for ya. Check out the play store though, you can filter by category and find the top sellers/downloaded to get some good ones