I organize my crontab by having group of tasks (the programs, the holidays, the housecleaning, etc). And of those groups, the events (the non recurring tasks) come last. So I just list the crontab (crontab -l) and the list of things to come print to the screen, that block being at the end of the file. It's hard to do better than a text file to list things. :)

I don't know if there is a program that lists like "what is coming this month" if you really want to filter out the rest, but it should be easy enough to write, given the format of cron rules:

crontab -l | grep '*' | awk '{print $4 "," $3 "," $2 "," $1 " " $0 }' | sort -n | grep -E "^$(date '+%-m')"

• crontab -l : list the crontab
• grep '*' : keeps only rules (removing blank lines and comments)
• awk […] : print the whole line ($0), prepend by the 4th field (the month), the 3rd (the day), the 2nd (the hour) and the 1st (the minutes)
• sort -n : sort everything numerically, so that all tasks are now in their execution date order (I made awk seperate the fields with a , character so it keeps sorting numerically past the first number)
• date '+%-m : prints the current month, not zero padded (thanks to the '-')
• grep -E '^date' : keep only lines which starts with the current month number

You put that in a script (like ~/bin/upcoming_events) and you're done. And then, you can call it from cron every monday get what's coming next mailed to you. :)

This could but refined further to display dates in a more friendly format. But as usual, Unix is your friend. :)