Here's a back-to-basics question for you guys. I just want to make sure I'm not missing anything.

My understanding is that:

"Mi legas" can mean "I read" and "I am reading."

"Mi legis" can mean "I read," "I did read" and "I was reading."

"Mi legos" can mean "I will read" and "I will be reading."

Am I missing any other possible meanings/translations or is that the full range of these three verb forms? Are there any nuances that I would need to be aware of?

Don't try to find a 1-to-1 correspondence between English tenses and Esperanto tenses. Translate the meaning, not the words. This does not only relate to Esperanto, but to any language.

nornen:Don't try to find a 1-to-1 correspondence between English tenses and Esperanto tenses. Translate the meaning, not the words. This does not only relate to Esperanto, but to any language.

Well I think that's what I'm trying to determine: Is there any more meaning packed into these three forms in Esperanto than the ones I've identified?

Sometimes the translation will be present perfect.
Mi loĝas ĉi tie jam 10 jarojn / I have been living here for ten years.

Li estas Esperantisto de multaj jaroj. He has been an Esperantist for years.

English has a verb system with five "tenses" and two aspects. I put tenses in parenthesis because future is not a real tense in the sense of having a verb form of its own, rather it is expressed with the help of auxiliary verbs.

The tenses are future, present, simple past, perfect and pluperfect. The aspects are continuous and non-continuous. In theory you can create five times two, ten, verb forms for a single verb. In practice you use less because of all kinds of restrictions and special cases.

Note, that aspects are highly language specific and thus the English aspect system of continuous/non-continuous is not present in many languages, like in Esperanto. This means that there is not an 1-to-1 correspondence between English tenses and Esperanto tenses, as Nornen stated.

The Esperanto verb system can best be understood in terms of the four modes, modoj.
 

• i-modo
  
• reala modo
  
• u-modo
  
• us-modo or imaga modo

Only the real mode, reala modo, has tenses present, past and future, those -as, -is and -os endings. While Zamenhof himself used quite a lot compound verb forms with esti + participle, thanks to the early pioneer Kazimierz Bein (Kabe) simple verb forms are preferred nowadays.

La pasinta tempo or the -is ending shows a real action that ended before the time reference of the speech. If the time reference is not explicitly indicated, it is assumed to be "now". Thus mi legis denotes an action that ended sometime before "now". How to translate this into English, depends on the context. Possible alternatives are, but not limited to, "I read, I was reading, I had read, I had been reading".

La nun-tempo or the -as endings shows a real action that takes place now or at the time of reference if explicitly stated. The action may well have begun a long time ago, but the point is that it still happens now (cf. the example given by Sudanglo, Mi loĝas ĉi tie jam 10 jarojn). Thus for mi legas possible translations are, but not limited to, "I read, I am reading, I have been reading".

La venonta tempo or the -os ending shows a real action that has not yet begun. Thus for mi legos possible translations are, but not limited to, "I shall/will read, I am going to read".

Note, while the future is always uncertain, the "real" in the -os ending denotes an action that can reasonably be expected to happen. For instance Morgaŭ estos dimanĉo (I am writing this on saturday) carries the idea that by all expectations sunday will rise. This is in contrast to the us-modo which denotes a hypothetic situation. What throws many off, is that the us-modo is timeless. This is illustrated best with the following example:
 

• Se Zamenhof posedus la ĉinan, Esperanto estus malsama.

where the two us-modo verbs must be understood to refer to the past resp. present time or the sentence does not make sense (I leave the analysis as an exercise).

English has a verb system with five "tenses" and two aspects. I put tenses in parenthesis because future is not a real tense in the sense of having a verb form of its own, rather it is expressed with the help of auxiliary verbs.

Well, that's one way of looking at it. I personally prefer to see it this way: English has three tenses (present, past and future) and two mutually independent aspects, to wit "continuous (progressive)" and "perfect (actually more like perfective)". Let's call the tenses PRE, PAS and FUT, and the pairs +CON and -CON, and +PER and -PER. This yields all 3 * 2 * 2 = 12 tense-aspect froms of English:

PRE -CON -PER = present: I see.
PRE -CON +PER = present perfect: I have seen.
PRE +CON -PER = present continuous: I am seeing.
PRE +CON +PER = present perfect continuous: I have been seeing.

PAS -CON -PER = past: I saw.
PAS -CON +PER = past perfect: I had seen.
PAS +CON -PER = past continuous: I was seeing.
PAS +CON +PER = past perfect continuous: I had been seeing.

FUT -CON -PER = future: I shall/will see.
FUT -CON +PER = future perfect: I shall/will have seen.
FUT +CON -PER = future continuous: I shall/will be seeing.
FUT +CON +PER = future perfect continuous: I shall/will have been seeing.

Actually, regarding tenses and aspects (aktionsarten) English is the most regular language I know. Obviously those 12 forms exist in three moods (indicative as shown, subjunctive and imperative) and two voices (active as shown and passive) which add up to a hypothetical (not all imperatives exist; most subjunctives are indistinguishable from the indicative) 72 forms. That's more than Volapuk.

@Nornen

That certainly is another way to look at it. However the regularity is questionable, because there are a lot of verbs that simply are not used in their continuous forms (be, want, need, love, hate and several more) or verbs which have different meanings depending on whether non-continuous or continuous form is used (appear, have, look and a couple more).

In any case I totally support your statement

Nornen:
Don't try to find a 1-to-1 correspondence between English tenses and Esperanto tenses. Translate the meaning, not the words. This does not only relate to Esperanto, but to any language.

Metsis:
Thus for mi legas possible translations are, but not limited to, "I read, I am reading, I have read, I have been reading".

Thanks for the detailed post. You lost me at this part, though.

I would think that "I have read" would be "mi legis," since the reading was done some time in the past.

For instance, if I asked someone, "Ĉu vi legis ĉi tiun libron?," and they said, "Mi legas tiun libron," then that would indicate to me that they are in fact in the middle of reading the book right now (for instance, the last time they set it down they were on page 53).

Please explain.

PrimeMinisterK:
I would think that "I have read" would be "mi legis," since the reading was done some time in the past.

Eh, that is an error from my part. I edited my reply.

As sudanglo has already pointed out somewhere else, the present perfect is a bit tricky: sometimes it translates as past, sometimes as present... There is no simple correlation.