In the spirit of supporting the retroclone publishers, and adding cool ideas to BECMI, I've decided to examine each of the games in turn, and grab at least one idea to tweak for use in a BECMI game. I'll also, of course, provide links to the download page and/or storefront site where you can acquire the game in question, if my teaser piques your interest.
First up is Caverns & Cavaliers, by WeaselFierce (Free PDF Download, Link:http://weaselfierce.webs.com/roleplaying.htm). WF introduces an interesting idea called Traits, whereby every few levels, a player can choose from a list of bonus abilities to add on top of the normal class abilities. In C&C, this serves somewhat of a custom class builder option, since the base classes are a bit more barebones than in BECMI, but the abilities are fun and minor enough to use without ruining game balance.
I suggest allowing the player to choose one Trait every 5 levels, including level 1 (so, levels 1,5,10,15,20,25,20,35) from the following list. The DM may add or remove abilities from the list as he sees fit for his campaign.
Trait Effect Weapon Expertise +1 to hit with a specific type of weapon (may be taken multiple times, either stacking the bonus for one weapon, or choosing a new weapon Linguist Character gains the ability to speak and read one additional language (may be taken multiple times) Defensive Reflexes -1 bonus to Armor Class (may be taken multiple times) Toughness +3 to total hit points (may be taken multiple times) Fast Healer Character heals an additional point of damage per full nights rest (may be taken multiple times) Lightning Reflexes +1 Bonus to initiative (may be taken multiple times) Alertness -1 bonus to personal surprise checks (may be taken multiple times) Brute +1 damage to melee attacks (may be taken multiple times) Devout Hunter +1 to all Turn Undead checks (may be taken multiple times) Eagle Eye +1 bonus to find secret doors checks Lucky Locksmith +5% to find and remove traps checks (may be taken multiple times)
Caverns & Cavaliers offers a bunch of other interesting ideas, such as custom class templates and advanced classes for experienced characters, it's definitely worth downloading and taking a look.