You have to google for this sort of thing. I have a list a mile long but it's mainly bookmarks

For German services, I only know of one commercial one. However there is a new one starting and you can get on the beta trial right now I think - I've listed it below. All these are free but some have a commercial upgrade.
Here are my favourites, there are plenty more but many of them scrape these anyway:
#1: KeywordDiscovery
This is currently the best and has taken over from WordTracker. It uses Mr G's DB so it's far more relevant now, plus it has better US results than WT. Free online version here:
www.keyworddiscovery.com/search.html#2: WordTracker
Used to be #1 but KD is a better choice now - but there are exceptions depending on your intended use. For example WT has a strong UK - Aus axis so if you're looking at the International English markets / spelling then WT can help. Free version:
http://freekeywords.wordtracker.com#3: Google Adwords external tool
Very good for several reasons: monster DB to draw on; interesting presentation; obviously, google-centric so it's very useful for checking G-specific issues; excellent one-page listing of alternatives. Here:
https://adwords.google.com/select/KeywordToolExternal#4: Google sktool
This G-tool tells you what's out there that G might send traffic to you for, if you rank for it. It scrapes KWs off your site then matches them to query variations. Excellent for an established site, to tune better & to look for opportunities.
www.google.com/sktool/#There are plenty of others but there is a limit to the number of hours in the day. Overture is RIP by the way and had been for a long time even when it was working

Deutsch: new beta trial here:
er, sorry, can't find that URL now. Later maybe.
Here are a couple of useful De. search-related sites though:
www.suchmaschinentricks.de www.at-web.deHope that lot was of use. You don't need a bunch of keyword tools unless you have exotic requirements, 3 or 4 does the trick.