There are many ROMs, some for just few specific devices, some for a wide range of phones... the choice of which you want is up to you. Since I'm a Desire user, I will mostly give you Desire ROMs, but that doesn't mean I'll leave other devices out of the question.
Let's head over to the first ROM we're going to present here.
LeeDrOiD is a Sense ROM (which means it's got HTC Sense UI), slightly modified and heavily optimized. There are only two ROMs made by this guy : for HTC Desire (Bravo) and for HTC Desire HD (Ace). The latest version is v3.3.3, for the Desire HD (also abreviated by DHD -- like the Dialing Home Device in Stargate, if you're a fan :D). The latest for the Desire is v3.3.3, too -- ported from the Ace build : with Sense 3.0 and stuff.
I am telling you, I used this ROM for about two months and I had no truble with it, at all!
It is based on Android 2.3.3 Gingerbread, and its core features are :
-advanced power menu
-extended quick settings (toggles in pulldown)
-modified Wi-Fi (powerful driver, that is)
-CRT TV animation for screen on/off
-BIOS-like start-up animation
-you can open up to 20 tabs in browser now
-battery life improved
-RAM management improved
-lots of speed tweaks
-fly-in animations for pop-up windows
-deodexed & zipaligned on boot
-huge APN list (I didn't know the proper settings for my carrier before using this ROM, to be honest)
-CIFS & CIFS Manager
-Sense 3.0-like USB Selector
-Sense 3.0 Task Manager
-and, most important : Sense 3.0 add-on (can be flashed manually in Recovery), which enables lockscreen widgets such as Clock, Weather, Slideshow and Stocks and, of course, the lock ring -- Sensation style.
There is also an A2SD function in this ROM. You must choose which version you want to use : the Data++ or A2SD (each for one variation of HBoot).
The Data++ version works ONLY on these HBoots : CM7r2, Bravo N1Table, Bravo Data++ or Bravo Sense (all four enable more storage for applications data).
The A2SD++ version works ONLY on the Bravo Stock Hboot.
For this ROM, you will have to partition your SD-card (above class 4 is reccomended) in this way, with either ROM Manager, ClockworkMod Recovery or GParted (Linux environment) : 1 GB EXT3 partition (or EXT4, if you have a class 10 card, like me) and the rest FAT32, of course. And don't make any partition for swap -- you won't be needing it.
Also, when you first flash this ROM, make sure you wipe EVERYTHING in Recovery. That means data (factory reset), cache and dalvik cache. As always, I suggest you do it twice (you may never know).
The advanced power menu
Now, the images above are the official ones that the developer has published. You can find more images as well as the full changelog and download links at the XDA forums topic.
LeeDrOiD also has a mini-site, but I think it is somewhat outdated. The reason for that is because I see the latest ROM version for the Desire is stated to be 184.108.40.206, which I know was in June... before the v3.3.3-R5 port. Check it for yourself at LeeDrOiD's homepage, if you will.