When T-Mobile finally updates their Curve OS to 4.3, HTML support will be built-in. Supposedly, this will happen sometime soon (but who really knows)....
I use BBSmart, it seems to be a toss up between Empower and BBSmart though, BBSmart has more options, Empower is a little bit faster.
Supposedly there is a free one, BMail or something like that, search around and you may find one to hold you over to OS4.5
Posted from my CrackBerry at wapforums.crackberry.com
If you're on BIS you'll be waiting for quite awhile until your carrier upgrades their servers to give you the 4.5 functionality (whereas BES users will have the updates more or less as soon as 4.5 comes out). So if you need/want HTML mail now try BBSmart or Empower (both have trials) and several of us actually own both.
One more note on the topic. I tried to download empower but was not able to. Since i'm a BES user and my company doesn't allow third party downloads i'm stuck with the OS and waiting for the update. If you are a BES user, you might want to confirm with your IT department before you get excited over nothing or just try to download it and see what happens. I was excited and them quite irritated when I could not download empower.