I use bestskinsever its pretty much the exact same thing as invivibleshield except for 10 bucks you get full body coverage instead of 20 just for the screen.
And yes if you want a super smooth slick cover stay away from BSE and IS cause they do have a kinda tacky feel but I LOVE it on the battery cover. It makes it feel kinda grippy and makes it look really shiney. And after a couple weeks they do get less tacky feeling but it never completly goes away.
BSE also has AWESOME customer service. it took 2 days to get my first one and after I installed it it had a rough lookin spot in the hardware button cover (May have been a fingerprint from my install?)
So I emailed them and told them about it nicely, not really overly caring if they did anything about and 2 days later there was a total brand new skin in the mail.
As for a cover I use this one-->
http://cgi.ebay.com/HTC-TOUCH-DIAMON...3A1%7C294%3A50
I found it for 7.99 with free shipping so you prolly can to if you look through a few pages. I only use it for work cause I leave my phone out on top of my toolbox with Pandora playing and Im afraid it will get knocked off, but for everyday use I just trust the BSE.
Be careful though, the first one I got didnt fit at all so I emailed them and complained and the 2nd one fit perfect.
AND.. Thats my opinion on the subject!