For the remote, I picked up a
Logitech Harmony 300 for pretty cheap... it works rather well, but it doesn't have as many programmable macros as the regular harmonies have. I have my TV, HTPC, a receiver, and a DVD player (kinda moot with the HTPC but the wife uses it as a CD player sometimes). I already had an USB IR receiver from a previous HTPC build, so one would need to pick one up if they didn't already have one (some laptops and some htpc cases have them built in). With my current software setup, it's rare that I need anything besides the remote, but I do have a logitech wireless keyboard in case I need it (although most of the time, with software adjustments, I just remote desktop from my other computer).
For software, I run Windows 7 and launch Media Center, and then use Media Browser to handle all my videos and movies. I didn't bother hooking up a tuner card since I just download everything anyway. I looked into Windows 8 (since I could've gotten it for cheap, plus gotten the Media Center add-on for free at the time), but people were saying that Media Center had all the same bugs that it had in Windows 7, with the caveat that Media Browser no longer worked with it (not sure if any of this has changed since I looked into it 2 months ago). Overall I'm happy with my software setup. The software is very user friendly and easy to figure out (a.k.a., wife and out-of-town family-visiting friendly). The setup process is straightforward as well.
I used to use an old Inspiron 9300 for my HTPC, but it was a bit sluggish. I have a desktop tower sitting next to my entertainment center now, and most of my friends commented that they didn't even notice it was there when they asked how I got all the videos on my TV.
On a side note, there's a free android app called myRemote that works rather well... you install a program on the computer, and you can control your HTPC with your phone (or other android device). It includes a mouse function (works like a touchpad) and a basic keyboard entry section. Comes in handy if you just need to do something quick and don't wanna bother with the mouse/keyboard.