Google states no more than 100 but I personally try and keep it no more than 20 as anything higher can look a mess - IMHO.
You won't get penalized.. IT's your website you can add as man as you want but it won't look attractive. Plus if you are selling links then its a bad idea. With eevery outgoing link you have the total value of the link goes down.
Sometimes it is more profitable for you have to a few links sold at quite a bit of money than a bunch of links sold at a little money. So, my advice to you is to keep a few outgoing links because you might make more money.
As other suggest, keep it as low as possible, the higher links will results in your site being catched for linkfarm.