Do you know if there are any grammar exercise books for Greek as a foreign language? I would love to get more practice, after years of speaking without paying much attention to grammar.

The only Greek grammar that I have seen and that I own is "Greek: An Essential Grammar of the Modern Language (Routledge Essential Grammars)". I don't know if it's similar to Practical English Usage...

If anyone is interested in Greek grammars, I found at least the ones below on the internet. They're all only in Greek, like Alexander said you can find Greek school books freely available on the internet.

This one says it's for intermediate learners of Greek as a foreign language:

http://www.ilsp.gr/files/Basic_Greek_Grammar.pdf

A classic when it comes to grammars of Modern Greek:

http://1dim-oraiok.thess.sch.gr/docs/grammatiki_neas_ellinikis_Triantaffilidis.pdf

A grammar book for Greek secondary schools is available here:

http://ebooks.edu.gr/new/books-pdf.php?course=DSGYM-C107

(scroll to Γραμματικη Νεας Ελληνικης Γλωσσας (Α-Β-Γ Γυμνασιου) - Βιβλίο μαθητή)

That website also has lots of other school books both as websites and pdfs - Greek literature, ancient Greek etc, but all only in Greek of course.

And a grammar book with exercises:

http://taexeiola.blogspot.fi/2013/03/grammatiki-neoellinikis-glossas.html

There is a school's grammar book which has literally everything about Greek grammar.
The only problem is that it is written in Greek.... so you need to have some level of Greek before you can use it.
On the other hand the good thing is that this is free because it was printed by the Greek public institution which prints the school books.
I have it in pdf if anyone is interested.

Eka, thank you my friend. Yes i was advised too with the "Greek: A Comprehensive Grammar of the Modern Language ".

"http://www.amazon.com/Greek-Comprehensive-Language-Routledge-Grammars/dp/041559202X/ref=pd_sim_b_5?ie=UTF8&refRID=0614Y1Q8CPVX430QCZ44"