I'd like to tag along as I've been looking on and off at other stamp sets but not chosen any yet.
DS loves the letter stampers he has. I picked them up at The Range, 3 sets (so 3 different fonts, one is upper case, one lower and one is a curlicue type fancy letters). They were smaller than I had planned on getting but actually turned out to be brilliant, great for fine motor and because they are quite small we can fit "Happy Birthday" etc onto a card without difficulty which I think would be hard with larger letters. DS likes to have a real purpose to his 'work' so making birthday cards for friends is more his thing than stamping for the joy of it iyswim.
I'm having a hard job remembering if I got them last year or the year before but certainly he has had more interest since turning 2 and they've been used regularly this year. Can't find them on the Range website but they are basically like these:
http://www.ebay.co.uk/itm/Dovecraft-Mini-Alphabet-Rubber-Stamps-30-Wood-Mounted-Stamps-Per-Set-/181254182623?var=480290390961&_trksid=p2054897.l4276The packaging is less attractive than the Melissa and Doug but they work and depending on your budget you could get several sets of letters, shapes, messages, ink pads and blank cards or paper stock for the same price as the M&D set.
Ink pads in the Range come in different prices, I don't really know the difference between them but was very surprised that I was able to choose several colours for a fraction of the cost of whatever the other brand was. Worth shopping around, they don't seem to be on the range web site either but I know they still sell them, and it's better to get the grown up type ink pad rather than a little kiddie one that is poorer quality and doesn't last. Ours have not run out after a full year of stamping.