Polk Audio
I had a few generations ago a line of RTi's, they were fantastic, anchored by RTi 70's in cherry wood which I wish I never sold those towers; they were excellent in their price point.
However, the LSi line is awesome. They are less efficient and 4-Ohm speakers, but any sound/music/theater guy worth his salt would have a receiver/amp that is good enough to play them plenty loud in a small to medium size room.
If you are looking to play at concert levels (and live somewhere where you can get away with it), then yes, you might want a separate amp; especially if you have a room over 500 SF.
I've always powered my LSi's with HK receivers, and have never felt short on power in a 5.1 setup. I've been recently (the last few days) experimenting with my AVR 745's 7.2 capabilities (maxing out the outputs), and I must say, it's definitely working harder. I don't live in a place where I can easily reach volume levels that bother the HK's though. I'm sure an Onkyo 7xx or higher would be fine. I'd trust Onkyo, HK, and Denons with 85x7 or more power for typical users duties. Maybe throw in Yamaha's rated 100x7 or better.
I must say as far as RTI's go.... I thnk the older one's were better, before they made them far brighter. I had the RTI 70's, 38's, and CSi 40 in an awesome 5.1 setup. I'd put those RTI's up against any iteration previous or after in the RTi lineup.