Hi Fmaz, welcome to AVS!
First, I'm glad to hear you really like your UT50 because that's what I'm looking to buy soon. I've pretty much just finished my home theater with the exception of a nice big TV. For a blu-ray player I recommend Panasonic 220. I haven't read up on this years models, but the 210 from last year was a great model. Otherwise the Sony S590. I have the S580 and it was supposed to be neck and neck for the best players last year, excluding Oppo of course. I think either of those are around $150 this year, while last year they were closer to $200. For a receiver, I'm very happy with my Yamaha V667 (2 year old model), I think the x67 series was the last to have multi-channel input, I don't know if that's important to you or not, but it seems that feature is being phased out. If you ever plan on getting an amp to power your speakers then you'll want pre-outs on the receiver, I think for Yamaha it starts with either the 500 or 600 series. I purchased my receiver 9 months ago from Newegg as a refurbished unit and paid like 40% of MSRP, so refurbished is always a possible way to go to save money and get a great deal. Many folks here also like Onkyo, Denon, and Pioneer for receiver brands. Somewhere in the $600 range for a receiver will get you plenty of inputs for anything you might need. If you're planning on connecting a PC you'll always be able to use and HDMI port for video out but there are select receivers that have a VGA connector on them. For speakers, I don't know what you have or what you're looking for to be either an upgrade or just to replace them with something new, but I chose to go with Polk speakers for my set up and they perform very well. I have Monitor 40s for the fronts, Monitor 30s for the rear, and a CS20 (or is it a CS2? Whichever the older model is). The 30s and 40s are bookshelf speakers and the 30s have a mount on the back that you could hang them from a screw (or whatever the proper way to hang a speaker is). I think for my 5.1 speaker setup, with receiver, I probably paid about $1000 because I waited for good deals at Newegg. For a sub, I chose to DIY a Bill Fitzmaurice's Tuba HT sub. They cost about $500 in lumber and parts, including the driver and amp. If you like to do DIY projects then this could be a great option. The sub is quite large, it measures 36" H x 24.5" D x 36" W but it's supposed to be unrivaled by anything for the price. And it can shake the walls pretty easily. My living room is pretty small, it's 13' x 13' but I know a lot of members here have rooms closer in size to yours and can probably give better ideas on how to fill the space with sound better. I hope this helps and gives you some ideas for your new HT. Enjoy it when it's all finished!