Let me start :) hope this helps
1) open your picture in photshop
2) select Lasso tool and draw a circle in the middle ( near the edges of the photos depending how u want the vigenetting to be )
3) Select--> Invert Selection
4) Now Layer, add new adjustment layer, levels
5) now here is the tricky part. you`ll see output level on the new window that poped up, and there is a white indicator one the left and black one on the right. Slide the one on the left (white one) to the middle and you will see a vigenetting (black shadow) around your photos. Adjust it to your liking. click OK.
6) Layer tab again, add new adjustment layer, curves
7) now you`ll see a line which is somewhat like this / , what you have to do is pull the lines so it will be a 'S' shape.
TO be more elaborate here is what i did, move your cursor to the graft so your input is 64 and so is the output.
click on it and move it till it says input 75 output 63. you`ll see the bottom line curves downward. next again move your cursor to input and output 191, do the same till input is 180 output 202. click ok.
8) do the same, but this time select the new fill layer, and fill it with black colour. click ok.
9) next change your blending mode to hue, you`ll find it on top or your layer tab and set opacity to bout 40%.
10) there now you`ll see a photo with vigenetting and colours like Lomo. What you have to do next is flatten the image by right clicking on the layers tab on your work space.
And wala, theres a lomo-ed picture and what i usually do is adjust the hue/saturation of anythgin to your liking.
i got this tutorial from a web site but i forgot the URL and the author. So if anyone sees it and thinks its your make sure you mesage me i`ll put the credits to you. But end of the day, there are various ways of lomo-ing a picture and make sure you create an action button for this. Else you`ll end up repeating everythign again and again.
Hope this helps, quetions you can put it up here and i guess there will be lots of help around.