I would start with games designed around the keyboard+mouse.
These tend to be games in the RTS/4x/Sim games and maybe some Tactical Turn-based RPGs, as well as FPS games. BUT, before jumping to FPS which will require a bit more accuracy with your mouse input, I would start with something a little more slower pace so you can get use to the feeling of mouse and keyboard. Personally, I would start with Civ5 or a Sim game in the vein of Cities:Skyline, Rollercoaster Tycoon (or if there are any modern equivelents), or even The Sims. These have a much slower pace than an RTS giving you plenty of time to make your actions without having to worry about the encroaching enemy.
You lso have options like X-Com which is a goog tactical turn based RPG complete with PC levels of difficulty, however, since it is turn-base, you will have plenty of time to get comfortable with the mouse.
Stepping up is FPS. FPS's while now dominant on all platforms, were originally designed for the PC, and the PC really shines with FPS as there is no better way to control an FPS than with a mouse. Unfortunately, if you aren't use to a mouse, this might be a difficult adjustment, but if there is any way to learn, then it might be to get any FPS, drop it to it's easiest setting and just run through the game while trying to find the most comfortable way for you to play with a mouse and a keyboard.
A good thing to keep in mind, a keyboard and mouse has it's limits, and some people have different preferences on what type of games they prefer mouse and keyboard or prefer a controller with.
For example, most racing games, platforming games, beat'em up games, fighting games, and some third person games I prefer using a controller to play. Sometimes, depending ont he varrying levels of action in the game I will use a keybaord and mouse sometime, and in the middle of the game I will switch to a controller, like in the new Tomb Raider. During the platforming section, it was more comfortable to use a controller, but when there was a lot of action I would switch to keyboard and mouse for better aiming.
Play with what you are most comfortable, and if you want to learn how to be more comfortable with mousey keyboard, then once in awhile, instead of using a controller, try to use the mousey keyboard for a little.
edit: so many typos - sorry. I typed it all in a rush and now I don't have time to fix them all. Forgive my messy typing!