There is another top five list over at the Dwarf and the Basilisk about his top five "basic" (but actually classic) D&D modules.
Here are my top 5 TSR Basic Modules:
5. Horror on the Hill - A great meat and potatoes adventure and it has a dragon - that is awesome!
4. Veiled Society - My first urban adventure. This and X3 became by baseline for developing urban adventures.
3. Keep on the Borderlands - My first module. A great illustration of a micro-sandbox.
2. Night's Dark Terror - A great sword & sorcery feel with lost races and unknown horrors.
1. Lost City - Also has a great S&S feel. Lost City is a great example of showing a young DM how to do things. It gives some great ideas and fleshes out some of the levels but leaves a lot of stuff up to the DM and gives lots of areas to develop.