Before I got my 800XL, I had an Intellivision. Now many people know that the Mattel console had some very good sports games and I played the crap out of Intellivision Baseball. When I got the 800XL, there are a number of games and I still play some of them to this day!
HardBall! - just a great fun baseball game and I played thousands of two player games for this one. Its underrated and super fun. I love the fact that this was eventually made into a cartridge! I only had the diskette version in the "album style" case. I recall really getting to know the whimsical player names and you really got to know their abilities and quirks! It was almost like they had personalities.
MicroLeague Baseball - weird but fun game which is really more of a managerial simulation. The quirky Apple graphics (it must be an Apple II port) are good and the game is fun, but you really do need the key chart. I always played this one solo and it was fun. There were some expansion disks, but I don't recall having those back in the day (I'll have to check my originals--pretty sure I just had the main game). Still play it occasionally to current day!
Starleague Baseball - This one is by gamestar and it has fairly good graphics. The diamond is slightly askew from the Intellivision game, and gameplay is fun! I remember seeing advertisements for this game in Electronic Games magazine in 1983 and it just looked so sophisticated to me at the time!
RealSports Baseball - this might have been one of those 5200 conversions, but while I remember the game, I don't recall having played it much. The graphics sure looks spectacular! Anyone else have a perspective on this one?
Now I checked on Atarimania and there are a bunch of other baseball games... I was a baseball fanatic as a teen, so if I knew about them (or had access to them) I would have tried them. Are there any others worth getting into?
Baseball (several different games with this name)
Major League Baseball
All Star baseball
Baseball (Sears, Inhome, Aim)