Depends what interests you I guess. After my recent marathon I have reduced the weekly mileage a lot, and am starting to introduce some specific speed sessions so I can race some 10ks and 5ks though the summer, before doing a bit of base fitness in late autumn / early winter, ready for another marathon attempt next spring.
I'll be doing more swimming and strength training this summer too, just to mix things up a bit. You've done well to get a GFA in your first marathon, you must have trained really well, so just see where you're interests take you for the next few months.
I'm with stu on this one. I used a casio digital watch that I bought from amazon for about £6 a couple of years ago. It doesn't show pace or tell you what distance you've covered but if you're starting out and just want to know how long you've run for, and to record some splits over a measured distance outside, it's ideal.
The garmin I later bought was basically just a toy to treat myself.